TESTING 

FOE   THE 

FLOTATION  PROCESS 


BY 


A.    W.    FAHRENWALD,    MET.E.,    E.M. 
it 

PROFESSOR  OF  MINING  AND  METALLURGICAL  ENGINEERING, 
NEW  MEXICO  STATE  SCHOOL  OF  MINES 


FIRST  EDITION 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 

LONDON:    CHAPMAN  &  HALL,   LIMITED 

1917 


3 


COPYRIGHT,  1917, 

BY 
A.  W.   FAHRENWALD 


To  His  WIFE 
LOLA   ELLSWORTH   FAHKENWALD 

THIS    BOOK    IS    DEDICATED    BY 

THE  AUTHOR 


372710 


PREFACE 

This  work  was  undertaken  with  the  object  in 
view  of  furnishing,  as  far  as  possible,  the  re- 
quired information,  to  give  students  and  any 
one  else  testing  for  the  flotation  process,  a  suffi- 
cient insight  to  conduct  experiments  in  an  in- 
telligent manner. 

The  theory  of  flotation  has  been  taken  up  in 
a  general  way,  no  effort  being  made  to  advance 
any  special  theory.  Those  which  have  been 
most  strongly  emphasized  have  been  discussed 
quite  fully  and  the  reader  is  left  to  decide  for 
himself  whether  flotation  cap  be  satisfactorily 
explained  by  any  one  of  them. 

The  knowlege  of  the  effect  of  oil,  acid,  and 
other  reagents  is  absolutely  essential  to  the 
experimenter,  and  these  have  been  taken  up 
with  the  object  in  view  of  throwing  light  on  the 
reason  for  their  use. 

To  those  who  have  contributed  to  the  useful- 
ness of  this  book,  I  express  my  extreme  indebted- 
ness. The  work  of  0.  C.  Ralston  and  Glen  L. 
Allen  has  been  frequently  referred  to  and  the 
material  of  Chapter  VI  is  largely  taken  from 
their  invaluable  article,  "  Testing  Ores  for  the 
Flotation  Process." 

I  am  especially  indebted  to  my  wife  who  has 
made  this  compilation  possible  by  her  aid  in 
preparing  the  manuscript. 

If  this  book  aids  those  testing  for  the  flotation 
process  its  purpose  will  have  been  accomplished. 

A.  W.  FAHRENWALD. 


CONTENTS 

CHAPTER  PAGE 

I.   CONCENTRATION  BY  FLOTATION 1 

II.   CLASSIFICATION  OF  THE  FLOTATION  PROCESS  4 

III.  THE  THEORY  OF  FLOTATION 7 

IV.  THE  FLOTATION  OF  OXIDIZED  ORES 79 

V.   OIL  AND  OTHER  REAGENTS  IN  FLOTATION..  86 

VI.   TESTS 110 

VII.   COST  OF  FLOTATION 151 

VIII.  FORMULAS  AND  TABLES 155 

INDEX.  .  169 


TESTING  FOR  THE 
FLOTATION  PROCESS 


CHAPTER  I 
CONCENTRATION  BY  FLOTATION 

Due  to  the  lack  of  a  definite  and  formulated 
state  of  the  art  of  flotation  a  great  deal  of  testing 
is  necessary  before  an  .ore  can  be  treated  on  a 
large-scale  practice. 

The  process  of  reducing  the  bulk  of  an  ore 
by  decreasing  the  percentage  of  gangue  in  it, 
and  thus  increasing  the  percentage  of  mineral 
content,  or  what  is  usually  known  as  the  con- 
centration of  the  ore,  is  both  an  important  and 
interesting  part  of  metallurgy.  Increasing  the 
percentage  of  valuable  substances  in  the  ore  is 
brought  about  by  separating  the  mineral  from 
the  gangue.  Such  a  separation  was  effected, 
until  about  the  end  of  the  nineteenth  century, 
by  mechanical  devices,  such  as  jigs,  tables,  and 
vanners,  where  the  separation  takes  place  in 
virtue  of  the  weight  of  the  sulphide  as  compared 
with  that  of  the  gangue.  There  are  also  other 
methods  of  separation,  the  processes  depending 
upon  one  or  more  of  the  different  physical 
properties  of  the  valuable  and  waste  material. 
The  difference  in  the  specific  gravity  of  a  mineral 
and  a  rock,  or  of  minerals,  affords  a  very  safe 
1 


2  CONCENTRATION  BY  FLOTATION       . 

and  sure  way  of  separating  them  from  each 
other,  the  separating  depending  entirely  on  the 
difference  in  the  settling  powers  of  the  different 
kinds  of  particles  in  air,  water,  or  any  other 
medium.  Other  properties  of  minerals  are  also 
taken  advantage  of,  as  electro-conductivity, 
magnetic  susceptibility,  etc. 

At  the  present,  however,  another  method  of 
concentration,  called  "  Flotation  "  (a  definition 
for  which  is,  apparently,  hard  to  supply),  has 
attracted  the  attention  of  the  Mining  World. 
"  Flotation,  in  its  latest  phase,  is  a  process  of 
concentrating  ores  by  frothing.  When  crushed 
ore,  previously  mixed  with  water  and  a  rela- 
tively minute  addition  of  oil,  is  agitated  violently 
in  the  presence  of  air,  a  froth  is  formed.  This 
froth,  rising  to  the  surface  of  the  liquid  mixture, 
is  laden  with  sulphides  or  other  metallic  par- 
ticles, while  the  earthy  material,  or  gangue, 
subsides  to  the  bottom.  The  froth  is  thick, 
coherent,  and  persistent/'1 

"  The  flotation  process  for  the  concentration 
of  ores  is  a  method  by  means  of  which  one  or 
more  of  the  minerals  in  the  ore  (usually  the  valu- 
able ones)  are  picked  up  by  means  of  a  liquid 
film  and  floated  at  the  surface  of  a  mass  of  fluid 
pulp.  Here  they  are  separated  from  the  other 
minerals  which  remain  immersed  in  the  body 
of  the  pulp.  In  general  the  minerals  which 
are  floated  are  sulphides  of  metallic  luster,  but 

1  Description  given  by  the  Minerals  Separation  Metal- 
lurgists; it  is  a  description  denied  by  others,  more  par- 
ticularly those  using  the  Callow  machine. 


CONCENTRATION  BY  FLOTATION 

some  other  minerals  of  metallic  luster,  such  as 
graphite,  and  some  sulphides  with  adamantine 
luster,  such  as  sphalerite  and  cinnabar,  are 
amenable  to  treat  by  this  process."  : 

Some  of  the  points  to  explain  in  the  flotation 
process  are : 

1.  The  flotation  of  solid  particles  in  a  liquid 
the  specific  gravity  of  which  is  less  than  that  of 
the  solid. 

2.  The  preferential  flotation  of  the  sulphide 
portion  of  the  mass. 

3.  The  functions  of  the  reagents  used. 

1  "An  Explanation  of  the  Flotation  Process/'  by  Arthur 
F.  Taggart  and  Frederick  E.  Beach,  Bull.  A.I.M.E., 
August,  1916. 


CHAPTER  II 

CLASSIFICATION  OF  THE  FLOTATION 
PROCESSES 

The  apparatus  used  in  flotation  have  been 
classified  a  great  many  times, 1  so  it  has  not  been 
deemed  necessary  to  describe  the  various  ap- 
paratus used  in  the  flotation  process  but  only 
a  brief  classification  of  the  process  will  be  given. 

They  are  conveniently  divided  into  three  main 
classes  as  follows: 2 

1.  Film-suspension,  as  in  the  Wood  and  Mac- 
quisten  methods. 

2.  Oil  flotation,  as  in  the  Robson  and  Elmore 
bulk-oil  methods. 

3.  Bubble-leviation,  as  in   the   Elmore  Vac- 
uum,   Delprat,   Fromont,    and    Sullivan-Picard 
methods. 

The  third  class  can  be  further  subdivided  ac- 
cording as  carbon  dioxide  or  air  is  the  principal 
gas  utilized  for  making  bubbles. 

Finally,  the  air-bubble  methods  can  be  classi- 
fied according  to  the  way  in  which  the  air  is 
introduced : 

(a)  From  the  bottom  of  the  vessel,  as  in  the 
Callow  and  Owen  cells. 

(&)    By  being  entrained  or  dragged  into  the 

1  "The  Flotation  Process,"  by  T.  A.  Rickard,  Hoover, 
Stander,  and  Megraw. 

2  "The  Flotation  Process,"  by  T.  A.  Rickard,  p.  9. 

4 


FLOTATION  PROCESSES  5 

pulp  by  the  beating  of  paddles  or  some  other 
form  of  impeller,  as  in  the  Gabbett  and  Hoover 
mixer. 

(c)  By  escape  from  solution  in  water,  as  in 
the  Elmore  vacuum  machine  and  the  Norris. 

Another  classification  of  the  flotation  proc- 
esses is  that  given  by  H.  J.  Stander:1 

1.  The  process  in  which  mechanical  agitation 
and  oil  are  used  to  form  a  froth. 

2.  The  purely  surface  tension  process. 

3.  The  process  known  as  bulk-oil  flotation. 

4.  Acid  used  to  generate  gas  from  the  ore 
which  helps  in  the  formation  of  the  froth. 

5.  A  process  in  which  the  dissolved  air  in  the 
water,  with  or  without  the  help  of  oil,  is  used  to 
form  a  froth. 

6.  Pneumatic  flotation,  a  process  in  which  air 
is  forced  into  the  mixture  of  ore,  water,  and  oiL 

Another  classification  is  that  given  by  A.  F. 
Taggart  and  F.  E.  Beach,  and  is  as  follows:2 

1.  Film  flotation,  exemplified  by  the  Wood 
and  Macquisten  processes.  When  finely-ground 
ore  containing  sulphides  mixed  with  a  siliceous 
or  earthy  gangue  is  brought  gently  onto  the  sur- 
face of  a  body  of  water  in  a  direction  forming  an 
acute  angle  with  the  surface  of  the  water,  a 
considerable  portion  of  the  sulphide  constit- 
uent of  the  ore  floats  on  the  surface  of  the 
liquid  while  the  gangue  sinks. 

1  "The  Flotation  Process,"  by  H.  J.  Stander. 

2  "An  Explanation  of  the  Flotation  Process,"  by  Arthur 
F.  Taggart    and   Frederick  E.   Beach,   Bull.    A.I.M.E., 
August,  1916. 


6  FLOTATION  PROCESSES 

2.  Froth  flotation,  exemplified  by  the  Min- 
erals Separation  apparatus  and  the  Callow 
pneumatic  machine.  When  gas  bubbles  are 
introduced  into  a  fluid  pulp  composed  of  finely- 
ground  ore  and  water,  to  which  has  been  added 
(1)  a  small  amount  of  certain  oils,  or  (2)  a  small 
amount  of  certain  acids  or  acid  salts,  or  (3)  a 
small  amount  of  certain  alkalis  or  alkaline  salts, 
or  (4)  a  small  amount  of  a  mixture  of  oil  with 
acid  or  alkalis  or  alkaline  salts,  the  sulphide 
particles  in  the  ore  are  brought  to  the  surface 
on  the  gas  bubbles.  These  collect  in  a  froth 
heavily  laden  with  sulphide  particles.  The 
gangue  particles  are  not  brought  up  by  the 
bubbles  but  remain  in  the  mass  of  the  pulp. 

This  classification,  it  will  be  seen,  is  very 
similar  to  the  first,  leaving  out  "  bulk-oil  "  flo- 
tation, which,  of  course,  is  only  of  historical 
interest. 


CHAPTER  III 
THE  THEORY  OF  FLOTATION 

The  great  unsolved  problem  in  flotation  is 
the  identity  of  the  forces  that  do  the  floating. 
Some  say  that  it  is  surface  tension,  some  elec- 
tricity, and  some  molecular  attraction  between 
the  air  bubbles  and  the  metallic  particles;  and 
there  is  always  the  mystery  as  to  exactly  the 
part  played  by  oil.  In  fact,  there  has  been, 
little  agreement  among  writers  as  to  "  why  is 
flotation." 

It  has  been  found  that  in  order  to  grasp  the 
ideas  connected  with  the  flotation  process,  and 
to  be  able  to  conduct  experiments  on  any  given 
ore  with  any  degree  of  intelligence,  some  knowl- 
edge of  colloidal  chemistry,  physical  chemistry, 
and  electrical  principles  is  absolutely  essential. 
Those  who  have  been  dealing  with  the  laws  of 
gravity  in  connection  with  concentration  will 
find  it  to  their  advantage  to  review  the  theory 
of  colloids,  and  their  general  physico-chemical 
properties,  and  the  principles  of  elementary 
physics. 

In  the  many  articles  which  have  come  out 
in  the  Technical  Press  within  the  last  two 
years,  the  following  terms  have  been  used  fre- 
quently by  the  different  writers: 

(a)    Colloids,    (6)   Surface  Tension,    (c)   Con- 
tact Angle,  (d)  Capillary  Attraction,  (e)  Osmosis, 
7 


8  THE  THEORY  OF  FLOTATION 

(/)  Viscosity,  (</)  Adsorption,  (h)  Emulsification, 
(i)  Electrical  Phenomena,  and  (j)  Preferential 
Flotation. 

Colloids 

Since  the  size  of  many  of  the  particles  of  min- 
erals treated  by  flotation  is  of  the  same  magni- 
tude as  that  of  many  colloids  we  cannot  escape 
from  calling  ore-slime  "  coarse  suspension  col- 
loid "  and  must  apply  all  the  laws  of  colloid 
chemistry  to  our  problem.  Physical  chemistry 
has  been  a  recognized  tool  of  metallurgists  for 
some  time,  although  little  used  by  most  of  them, 
and  now  a  particular  branch  of  physical  chem- 
istry —  colloid  chemistry  —  is  beckoning  to  us 
alluringly.  All  questions  in  the  treatment  of 
ore-slime  should  be  studied  in  this  new  light.1 

Colloid  Terminology.2  —  Colloid  chemistry  has 
developed  a  system  of  terminology  of  its  own,' 
and  while  it  is  not  at  all  necessary  to  use  this 
terminology  in  discussing  the  subject  matter  of 
the  science,  many  of  the  terms  are  convenient 
and  are  now  thoroughly  engrafted  into  the 
literature.  Most  useful  is  the  concept  that 
regards  the  size  of  particle  as  due  to  the  "  degree 
of  dispersion  "  of  the  particulate  substance.  A 
decreased  size  of  particle  is  spoken  of  as  a 
greater  "  dispersion  "  or  the  substance  as  more 
highly  "  dispersed.'7  By  extension  all  suspen- 

1  "Why  Do  Minerals  Float?"  by  Oliver  C.  Ralston, 
Min.  &  Sci.  Pr.,  October  23,  1916. 

2  "Colloid  and  Colloidal  Slimes,"  by  Edward  E.  Free, 
Eng.  &  Min.  Jr.,  February  5,  1916. 


COLLOID  TERMINOLOGY  9 

\ 

sions  and  colloids  are  "  disperse "  (or  "  dis- 
persed ")  systems  of  "  dispersoids;"  the  par- 
ticles compose  the  "  disperse  "  phase  and  the 
medium  is  the  "  dispersion  medium."  A  true 
solution  possesses  a  molecular  or  ionic  degree  of 
dispersion  and  is  a  "  mol-  "  or  "  ion-dispersoid." 
These  terms  include  all  colloidal  systems,  re- 
gardless of  the  solid,  liquid,  or  gaseous  state  of 
particle  or  medium.  Colloidal  solutions  with 
a  liquid  medium  are  frequently  referred  to  as 
"  sols  "  (the  oppositive  term  of  "  gel  "  will  be 
discussed  in  a  moment).  If  the  medium  is 
water,  the  colloid  is  a  "hydrosol;"  if  alcohol, 
an  "  alcoholsol  "  or  "  alcosol,"  etc.  By  analogy 
with  the  systems  of  coarser  particles  the  solid- 
particle  sols  are  frequently  called  "  suspen- 
soids;"  those  of  liquid  particles,  "  emulsoids." 
The  terms  "  sol,"  "  suspensoid,"  and  "  emul- 
soid," with  their  compounds,  are  properly  ap- 
plied only  to  systems  within  the  assigned  col- 
loidal range  of  particle  size.  The  adjectives 
"  hydrophile  "  and  "  hydrophobe  "  are  remnants 
of  a  terminology  that  is  disappearing.  They 
were  supposed  to  refer  to  the  affinity  or  lack  of 
affinity  of  the  substance  for  water.  Roughly, 
they  are  equivalent  to  "  emulsoid  "  and  "  sus- 
pensoid  "  respectively. 

Much  confusion  has  arisen  from  a  loose  use 
of  the  terms  "  sol  "  and  "  gel  "  in  metallurgical 
literature.  As  noted,  a  sol  is  a  colloidal  solution 
having  a  liquid  medium  and  possessing  the 
essential  properties  of  liquids.  It  happens  that 
some  emulsoid  colloids,  of  which  gelatine  is  a 


10  THE  THEORY  OF  FLOTATION 

good  type,  have  the  property  of  setting  under 
certain  conditions  to  form  a  more  or  less  stiff 
jelly-like  table  gelatine.  These  jellies  are  known 
as  "  gels."  They  have  much  importance  in 
biology  and  some,  perhaps,  in  the  study  of  ore 
genesis,  but  it  does  not  appear  that  they  are 
important  in  metallurgy.  They  are  produced 
only  by  the  special  colloids  of  the  type  men- 
tioned, and  gelatinization  is  not  a  general 
property  of  the  colloidal  state.  The  resemblance 
between  a  jelly-like  thickened  slime  and  a  real 
gel  is  superficial  only,  and  any  consideration 
of  this  resemblance  in  metallurgical  investi- 
gations is  productive  merely  of  confusion.  A 
similar  confusion  has  arisen  through  the  use  in 
the  connection  of  the  concepts  of  amorphous  and 
crystalline  and  from  the  definition  of  colloidal 
substances  as  those  which  are  not  crystalline. 
It  is  open  to  question  whether  real  amorphity 
exists  except  in  fluids,  but  this  discussion  would 
lead  us  too  far  into  the  minutiae  of  modern  theo- 
ries of  matter.  For  present  purposes  it  is  enough 
to  recall  that  the  particulate  theory  of  colloids, 
as  we  have  developed  it,  includes  no  assumption 
as  to  the  amorphous  or  crystalline  nature  of 
the  particles,  and  it  may  safely  be  asserted  that 
none  is  necessary.  "  Gel  "  and  "  sol  "  and 
"  amorphous "  in  these  senses  could  be  well 
spared  from  metallurgical  terminology. 

The  Concept  of  Colloid  Chenystry.1  —  Colloid 
chemistry  is  not  the  study  of  colloid  materials 

1  "Handbook    of    Colloid    Chemistry,"    by    Ostwald 
Fischer. 


. 
THE  CONCEPT  OF  COLLOID  CHEMISTRY      11 

but  that  of  the  colloid  state  of  materials.  "  Col- 
loid "  is  not  a  chemical  entity  like  salt,  acid,  or 
base,  oxidizing  like  mechanical  heterogeneity. 
The  concept  "  colloid "  does  not  even  corre- 
spond to  that  of  "  precipitate  "  since  only  special 
forms  of  precipitates  may  be  termed  "  colloid." 
Nor  may  "  colloid  "  substances  be  discussed  as 
we  discuss  "  radio-active  "  substances,  for  radio- 
active properties  are  more  closely  associated  with 
certain  chemical  compounds  showing  definite 
properties  (high  atomic  weight,  etc.)  than  are 
the  colloid.  Like  considerations  hold  when  we 
try  to  parallel  the  colloid  condition  with  the 
"  liquid  crystalline,"  though  as  our  knowledge 
has  increased  we  have  found  the  latter  state 
less  and  less  directly  connected  with  definite 
chemical  compounds.  In  the  same  sense  "col- 
loid phenomena  "  are  not  to  be  regarded  as  due 
to  the  properties  of  colloid  materials  but  rather 
as  characteristic  of  any  material  observed  in 
the  colloid  state.  The  difference  between  these 
two  definitions  will  perhaps  be  clearer  if  we 
compare  colloid  chemistry  with  thermo-chem- 
istry.  Just  as  the  latter  is  not  a  study  of 
"  warm  "  and  "  cold  "  materials,  but  a  study 
of  the  thermal  condition  of  the  material  and  its 
changes,  so  colloid  chemistry  is  not  a  descrip- 
tion of  individual  colloid  materials  but  treats 
of  the  properties  of  which  colloid  systems  are 
but  examples.  Colloid  chemistry  deals  with 
the  relations  of  the  surface  energies  io  other 
kinds  of  energy  as  shown  in  an  especially  charac- 
teristic way  in  dispersed  heterogeneous  systems. 


12  THE   THEORY  OF  FLOTATION 

Thus  viewed,  colloid  chemistry  appears  as  a 
branch  of  physical  chemistry  coordinated  with 
electro-,  thermo-,  photo-,  radio-chemistry,  etc., 
in  other  words,  with  sciences  which  also  treat 
of  the  relations  of  one  kind  of  energy  to  others. 


CLASSIFICATION  OF  COLLOIDS 


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14  THE   THEORY  OF  FLOTATION 

Properties  of  Colloids.  —  How  do  we  know 
when  we  are  dealing  with  a  colloid?  This 
question  can  best  be  answered  by  presenting  the 
elementary  properties  and  the  experimentally 
observed  behavior  of  colloid  substances. 

1.  Colloid  properties  are  in  no  way  connected 
with  substances  of  definite  chemical  composition, 
in  other  words,  "  the  colloid  state  is  independent 
of  the  chemical  composition  "  and  we  can  speak 
of  colloids  only  as  we  speak  of  crystal,  amorphous 
substances,    soluble   and   insoluble    substances, 
or  better  still  of  gaseous,  liquid,  and  solid  sub- 
stances. 

2.  All  substances  can  appear  as  colloids  under 
appropriate  conditions.1 

3.  Only  one  law  has  thus  far  been  deduced 
governing  the  relation  between  chemical  con- 
stituents and  colloid  state:    the  more  complex 
chemically  the  compound,  the  greater  the  proba- 
bility that  it  is  in  a  colloid  state. 

4.  Typical  "  mechanical  suspensions  "  of  sub- 
stances but  slightly  soluble  in  liquids,  as  sus- 
pension of  quartz,  kaolin,  or  oil  in  water,  are 
turbid  in  transmitted  light,  and  their  individual 
particles  can  be  recognized  under  the  micro- 
scope.2 

If  no  microscope  is  available,  filtration  is  the 
next  simplest  method  by  which  a  suspension 
can  be  recognized.  Ordinary  filter  paper  holds 

1  Depending  upon   experimental   conditions   one  and 
the  same  chemical  compound  can  appear  either  as  a  col- 
loid or  a  non-colloid. 

2  Though  sometimes  only  with  high  magnifications  and 
special  optical  means. 


PROPERTIES  OF  COLLOIDS 


15 


back  particles  having  a  diameter  greater  than 
about  5ju;  a  hardened  filter  (Schleicher  and 
Schull,  No.  602,  e.h.)  those  about  2  p  in  diameter. 

TABLE  I.     SIZE   OF  PORES  AND  FILTERS 

(According  to  H.  Bechhold.) 


Filter. 

Average  size  of 
pores  (permea- 
bility to 
water). 

Size  of  largest 
pores  (permea- 
bility to  air). 

Ordinary  thick  filter  paper.  .  . 

3.3/i 

Filter  paper  No.  556  (Schleich- 
er and  Schull) 

1  7  ju 

Filter   paper   No.    602    (extra 
hard,  Schleicher  and  Schull) 
Chamberland  filter  

0.8a-1.3M 

1-1.  5  M 

0.23-0.  41  fji 

Reichel  filter  

0.16-0.  175  M 

Clay  cylinders  or  so-called  Pukall  filters  which 
are  frequently  employed  bacteriologically  will 
even  hold  back  particles  0.4  to  0.2  /z  in  diameter.1 
When  applied  to  emulsions,  that  is,  suspensions 
of  droplets  in  a  liquid,  filtration  is  successful 
only  when  the  suspended  droplets  are  not  molec- 
ularly  deformed  during  filtration. 

5.  True  solutions  may  be  distinguished  from 
colloid  solutions  by  their  optical  differences. 
A  liquid  which  is  not  chemically  homogeneous 
and  which  is  not  in  coarse  suspension  is  seen  to 
be  turbid;  we  may  suspect  that  it  is  a  colloid 
solution.  The  existence  of  a  slight  turbidity 
may  be  recognized  on  inspection  of  a  rather  thick 

1  For  details  regarding  permeability  and  size  of  pores 
in  various  filters,  see  H.  Bechhold,  Zeitschr.  f.  physik. 
Chem.,  64,  328  (198). 


16  THE  THEORY  OF  FLOTATION 

layer  of  the  liquid  in  a  thin-walled  glass  vessel 
against  an  opaquely  black  background. 

A  far  more  delicate  method  of  demonstrating 
the  presence  of  a  very  fine  turbidity  lies  in  the 
use  of  the  so-called  Tyndall  phenomena.1  Ex- 
traordinarily fine  turbidities  can  be  rendered 
visible  by  such  means;  in  fact  this  holds  true  to 
such  an  extent  that  special  measures  become 
necessary  if  we  would  obtain,  for  example,  an 
absolutely  "  optically  empty  •"  distilled  water; 
ordinary  distilled  water  regularly  shows  in- 
dividual dust  particles. 

Liquids  which  show  no  definite  Tyndall  light- 
cone  or  show  it  only  in  high  concentrations  are 
"  molecular  disperse  "  (true  solution)  solutions. 
Practically  all  colloid  solutions  give  a  positive 
Tyndall  effect. 

6.  Substances  in  the  colloid  state  practically 
do  not  diffuse  at  all;  at  the  best  they  diffuse 
with  extreme  slowness  when  compared  with  the 
behavior  of  substances  in  molecular  solution. 

7.  Dialysis,  a  process  closely  related  to  dif- 
fusion,   depends    upon    the    fact    that    animal, 
plant,  and  artificial  membranes  hold  back  sub- 
stances in  colloid  solution  while  they  allow  sub- 
stances in  molecular  solution  to  pass  through 
whenever  such  a  membrane  separates  the  liquid 
under    examination    from    the    pure    dispersion 
means.     The  dialyzer  distinguishes  colloid  from 

1  It  is  well  known  that  when,  for  example,  the  air  of 
a  room  is  intensely  illuminated,  say  by  sunlight,  from 
one  side  only,  dust  particles  are  rendered  visible  which 
cannot  be  seen  when  illumination  is  equal  on  all  sides. 


SUSPENSOIDS  AND  EMULSOIDS  17 

true  solutions  in  that  it  does  not  allow  the  former 
to  pass  through  the  membrane  into  the  outer 
liquid. 

Suspensoids  and  Emulsoids.  —  These  two 
classes  of  colloid  solution,  namely,  "  suspension 
colloids  "  (suspensoid)  and  the  "  emulsion  col- 
loids "  (emulsoids)  have  interesting  peculiarities. 
Some  of  importance  are: 

1.  The    viscosity    of    a    suspension    colloid, 
particularly    in    low    concentration,    is    imper- 
ceptibly greater  than  that  of  the  pure  dispersion 
means.     In   contradistinction,   the  viscosity   of 
an  emulsion  colloid  even  in  low  concentration 
is   much   greater   than    that   of   its    dispersion 
means. 

2.  The  viscosity  of  an  emulsion  colloid  generally 
increased  rapidly  with  decrease  in  temperature 
which  is  not  the  case  with  the  suspension  colloid. 

3.  It    is    characteristic    of    colloid    solutions 
that  the  substance  in  colloid  solution  may  be 
easily   precipitated   or    "  coagulated "    through 
various  agencies.     Electrolytes,  such  as  neutral 
salts,  are  particularly  effective.     The  suspension 
colloids    are    easily    coagulated    when    minute 
quantities  of  salts,  especially  those  having  poly- 
valent ions,  are  added  to  them,  while  the  emul- 
sion   colloids   are   precipitated    only    after   the 
addition  of  much  larger  quantities  of  salt.     This 
is   particularly   true   of   hydrosols    (that  is,   of 
colloids  having  water  as  the  dispersion  means). 
If,  for  example,  aluminum  sulphate  is  selected 
as  the  coagulant,   it  is  found  that  almost  all 
suspension  colloids  are  precipitated  by  this  as 


18  THE   THEORY  OF  FLOTATION 

soon  as  it  is  present  in  a  1  per  cent  concentra- 
tion. 

4.  Colloid  solutions  have  a  characteristic 
electric  behavior  which  explains  many  of  their 
peculiar  properties.  Most  substances  in  col- 
loid solution  assume  an  electric  charge  toward 
their  dispersion  means,  though  the  magnitude 
of  this  charge  varies  greatly.  Colloids  can  be 
separated  from  their  dispersion  means  by  capil- 
lary analysis.  If  the  lower  end  of  a  strip  of 
filter  paper  is  immersed  in  colloid  solution  one 
of  two  things  may  happen,  depending  upon  the 
character  of  the  electric  charge  of  the  colloid; 
if  the  colloid  carries  a  negative  charge  it  wanders 
up  the  strip  of  paper  along  with  its  dispersion 
means.  If  the  colloid  carries  a  positive  charge  the 
dispersion  means  continues  to  rise  to  the  normal 
height,  but  the  "  colloid  phase  does  not."  Oppo- 
sitely charged  colloids  precipitate  each  other.1 

The  character  of  the  charge  of  the  colloid 
phase  may  be  determined  by  noting  the  direction 
in  which  it  moves  when  subjected  to  the  action 
of  an  electric  current.2  To  do  this  the  colloid 
is  poured  into  a  U-tube  closed  with  corks  and 
provided  with  platinum  electrodes  which  dip 
into  the  solution;  a  few  storage  cells  may  suffice. 
I:  the  colloid  wanders  toward  the  anode  it  is 

1  If  two  typical  test  solutions  are  kept  in  stock,  for 
example,  a  positive  colloid  such  as  ferric  hydroxide  and  a 
negative  colloid  such  as  sulphur  or  arsenious  sulphide, 
the  charge  of  an  unknown  colloid  may  frequently  be  de- 
termined by  ascertaining  with  which  of  the  two  solutions 
it  yields  a  precipitate. 

2  Migration  in  an  electric  field. 


CONTROL  OF  COLLOID  CONDITION        19 

negatively  charged;    if  it  wanders  toward  the 
cathode  it  is  positively  charged.1 

Control  of  Colloid  Condition.2  —  Colloidality 
will  be  increased  by: 

1.  The   presence   of  small   amounts   of  free 
alkali  (except  lime). 

2.  Prolonged   grinding  or  long   exposure  to 
water  or  the  atmosphere. 

3.  Grinding  or  storage  at  high  temperatures. 

4.  The  presence  of  organic  material  such  as 
would  be  supplied  by  decaying  animal  or  vege- 
table matter. 

Colloidality  will  be  decreased  by  the  avoidance 
of  the  four  conditions  just  cited  and  also  by: 

1.  The  presence  in  solution  of  acids  or  of 
neutral  salts  or  of  certain  alkalis  in  certain  con- 
centrations. 

2.  Rapid  grinding  and  handling. 

The  relative  quantitative  importance  of  the 
various  factors  mentioned  and  the  decision  as 
to  which  should  be  selected  as  a  means  of  prac- 
tical improvement  will  depend  upon  local  con- 
ditions different  in  each  case.  In  general  the 
presence  of  organic  matter  has  the  most  effect, 
but  is  rarely  encountered.  Next  in  quantitative 
importance  is  the  presence  of  dissolved  acids, 
salts  or  alkalis.  Of  much  less  effect  is  the 
time  of  grinding  or  storage,  unless  it  runs  into 
years  and  of  still  less  effect  are  changes  of 
temperature  between  usual  limits. 

1  Above  remarks  largely  taken  from    "Handbook   of 
Colloid  Chemistry,"  by  Ostwald  Fischer. 

2  "  Properties  of  Slime  Cakes,  II,"  by  Edward  E.  Free, 
Eng.  &  Min.  Jr.,  June  24,  1916. 


20 


THE   THEORY  OF  FLOTATION 


Surface  Tension 

Definition.  —  Every  liquid  surface  in  contact 
with  a  gas  or  its  vapor  behaves  as  if  it  were 
under  tension.  The  value  of  this  contractile 
force  per  unit  width  can  be  measured. 

The  basic  factor  in  the  making  of  bubbles  is 
surface  tension.  This  is  the  force  that  causes 
the  surface  to  resist  rupture.  The  particles  at 
the  surface  have  a  greater  coherence  than  the 
similar  particles  within  the  body  of  the  liquid, 
or  the  tendency  of  a  liquid  to  reduce  its  exposed 
surface  to  a  minimum,  that  is,  the  tendency  of 
any  liquid  surface  to  act  like  a  stretched  mem- 
brane is  called  "  surface  tension." l 

Effects  of  Added  Substances.  —  Surface  ten- 
sion has  been  thrashed  out  pretty  thoroughly 
by  articles  appearing  in  the  Journals  of  the 
American  Chemical  Society  beginning  in  1908. 

Jour.  Am.  Chem.  Soc.,  Vol.       XXX,  No.    3,  Mar.,  1908. 


XXX, 
XXXIII, 
XXXIII, 
XXXIII, 
XXXV, 
XXXV, 
XXXV, 


7,  July,  1908. 
3,  Mar.,  1911. 
5,  May,  1911. 
7,  July,  1911. 

10,  Oct.,    1913. 

11,  Nov.,  1913. 

12,  Dec.,  1913. 


Some  of  their  conclusions  are  that: 

(a)  The  drop-weight  of  any  liquid  is  pro- 
portional to  the  diameter  of  the  dropping-tube. 
These  tubes  are  uniform  in  diameter,  thus  dif- 
fering from  the  ordinary  burettes. 

(&)    The  weight  of  a  drop,  other  things  being 

1  "First  Course  in  Physics,"  by  Millikan  and  Gale,  p. 
107. 


EFFECTS  OF  ADDED  SUBSTANCES         21 


the  same,  is  proportional  to  the  surface  tension 
of  the  liquid. 

(c)  It  is  possible  to  calculate  the  temperature 
at  which  the  drop-weight  would  become  zero, 
namely,  the  critical  temperature  of  the  liquid, 
for  at  that  point  the  drop  would  disappear, 
there  being  no  distinction  between  the  gas  and 
the  liquid. 

In  the  course  of  these  experiments  the  sur- 
face tension  of  a  number  of  organic  liquids  in 
aqueous  solution  was  determined  by  drop- 
weight  and  found  to  range  from  21  up  to  that 
of  water.  The  tabulated  results  cover  several 
pages  in  the  Journal: 

AQUEOUS   SOLUTIONS  AT  30°  C. 


Ethyl 
alcohol. 

Methyl 
alcohol. 

Amyl 
alcohol. 

Acetic 
acid. 

Formic 
acid. 

Per 
cent. 

Sur. 
ten. 

Per 
cent. 

Sur. 
ten. 

Per 
cent. 

Sur. 
ten. 

Per 
cent. 

Sur. 
ten. 

Per 
cent. 

Sur. 
ten. 

0.000 

71.030 

0.000 

71.030 

0.000 

71.030 

0.000 

71.030 

0.000 

71.030 

0.979 

65.600 

1.011 

68.120 

0.250 

53.712 

1.000 

67.756 

1.000 

69.816 

2.143 

60.847 

2.500 

64.845 

0.500 

46.157 

2.475 

63.995 

2.500 

68.024 

4.994 

53.137 

4.097 

60.294 

0.750 

41.247 

5.001 

59.435 

5.000 

65.706 

10.385 

44.668 

9.994 

53.661 

1.000 

37.631 

10.010 

53.500 

10.000 

62.061 

17.979 

37.311 

10.000 

48.817 

1.500 

32.504 

14.980 

49.451 

15.000 

59.197 

25.000 

32.941 

25.000 

41.809 

2.000 

28.667 

20.090 

46.455 

25.000 

55.190 

50.000 
75.000 
100.000 

26.521 
23.850 
20.756 

50.000 
75.000 
100.000 

31.843 
26.173 
21.073 

2.498 

25.726 

49.960 
79.880 
100.000 

37.109 
31.026 
25.725 

50.000 
75.000 
100.000 

48.112 
41.990 
35.281 

100.000 

22.296 

It  is  to  be  noted  that  in  all  cases  the  very 
first  addition  causes  a  very  considerable  lowering 
of  surface  tension.  The  decrease  in  the  surface 
tension  of  water  caused  by  the  addition  of  a 


22 


THE  THEORY  OF  FLOTATION 


small  amount  of  amyl  alcohol  is  especially 
striking.  Thus  the  presence  in  solution  of 
even  so  small  an  amount  as  0.25  per  cent  changes 
the  surface  tension  of  water  from  71.030  to 
53.7,  or  nearly  25  per  cent  at  30°  C. 

Morgan  and  Schramm  studied  many  concen- 
trations of  a  few  salts.  They  selected  the 
molten  hydrated  salts  for  this  purpose,  those 
salts  which  melt  below  50  degrees  in  their  own 
water  of  crystallization  being  especially  satis- 
factory for  this  purpose,  for  the  reason  that 
concentration  in  some  of  these  cases  could 
have  been  carried  to  supersaturation. 


10    15    20    25    30    35    40 
Gm.  salt  per  100  gm.  solution 

FlG.  1. 


45    50 


In  the  case  of  salts  which  they  studied  it  is 
plain  that  surface  tension  is  increased  by  the 
salts  introduced.  Where  calcium  chloride  was 
used,  the  surface  tension  was  increased  from 


SURFACE  TENSION   PHENOMENA          23 

71.03  to  102.57,  approximately  50  per  cent. 
Taking  a  few  specific  cases  it  is  noted  that  to  in- 
crease the  surface  tension  10  per  cent  it  would 
take  20  per  cent  CaCl2  at  30  degrees;  43  per  cent 
Zn  (N08)  at  45  degrees;  29  per  cent  NagCrC^  at 
30  degrees;  34  per  cent  N 3-282 03  at  40  degrees. 

The  fact  is  that  some  salts  elevate  while 
others  depress  surface  tension,  but  the  former 
predominate.  In  addition  to  the  salts  just 
mentioned  the  tartrates,  carbonates,  oxalates, 
citrates,  lactates,  and  a  part  of  the  acetates 
raise  surface  tension;  while  all  the  salicylates, 
the  butyrates,  part  of  the  acetates,  and  all  the 
acids  lower  surface  tension. 

Surface  Tension  Phenomena.  —  Many  mani- 
festations of  surface  tension  on  water  can  be 
cited.  Fill  a  tumbler  a  little  more  than  full 
and  the  water  will  have  a  convex  surface,  in- 
dicating that  there  is  some  force  at  work  to 
prevent  the  water  from  spilling.  Note  the 
cohesion  between  two  plates  that  have  been 
wetted.  Dip  a  camel's-hair  brush  into  water 
and  the  hairs  cling  together;  immerse  the  wet 
brush  in  the  water  and  the  hairs  separate. 
Watch  the  formation  of  a  drop  of  water  and  note 
that  it  behaves  as  if  enveloped  by  a  stretched 
membrane.  Water-spiders  can  be  seen  run- 
ning over  the  surface  of  a  pond  in  summer;  the 
spider  makes  a  visible  dimple  without  wetting 
his  feet.  The  surface  is  not  ruptured.  Clean 
a  piece  of  iron  wire  and  place  it  gently  on  the 
surface  of  distilled  water;  it  floats.  The  ap- 
parent attractions  and  repulsions  exhibited  by 


24  THE  THEORY  OF  FLOTATION 

small  floating  bodies  on  the  surface  of  a  liquid 
are  due  to  surface  tension.1  Thus  two  small 
pieces  of  wood  floating  on  the  surface  of  water 
rush  together  if  they  come  within  about  a 
centimeter  of  one  another.  This  is  due  to  the 
fact  that  the  angle  of  contact  between  water 
and  wood  is  less  than  90  degrees,  so  the  water  is 
slightly  raised  up  between  the  floating  bodies 
as  in  a  wide  capillary  tube  (Fig.  2).  The  pres- 


FIG.  2.  FIG.  2a. 

sure  in  the  liquid  between  is  less  than  in  the 
surrounding  mass  and  the  bodies  come  together. 
In  the  case  where  the  angle  of  contact  is  greater 
than  90  degrees,  as,  for  instance,  with  needles 
floating  on  mercury  (Fig.  2),  the  liquid  between 
the  bodies  is  depressed,  and  the  hydrostatic 
pressure  on  the  outside  forces  the  bodies  to- 
gether. 

The  Force  of  Surface  Tension.  —  The  force 
of  surface  tension  has  been  measured  by  as- 
certaining the  weight  that  can  be  suspended 
from  a  film  of  water  in  air.2  It  has  been  stated 

1  "A  Textbook  of  Physics,"  by  Watson,  p.  185. 

2  "A  Textbook  of  Principles  of  Physics,"   by  Alfred 
Daniel,  1911. 


THE  FORCE  OF  SURFACE  TENSION   25 

as  3J  gr.  per  inch,1  or  81  dynes  per  centimeter.2 
A  later  determination  is  given  by  Theodore  W. 
Richards  and  Leslie  B.  Combs3  as  72.62  dynes 
per  centimeter  at  20°  C.  Many  interfering 
factors  enter  into  the  determination  of  this  force. 

Surface  tension  varies  as  between  various 
liquids  and  fluids  in  contact,  an  example  being 
that  of  the  tension  separating  mercury  from 
water  amounting  to  418  dynes  per  centimeter, 
while  that  separating  olive  oil  from  air  is  only 
36.9  dynes.  The  surface  tension  of  an  oil-water 
surface  is  only  14  as  compared  with  the  73  of  an 
air-water  surface  at  a  temperature  of  18°  C.4 
While  the  film  of  oil  on  water  may  be  only  one 
molecule  thick,  or  one  twenty-five  millionth  of 
an  inch,  it  will  suffice  to  reduce  the  effective  pull 
of  the  water  from  73  to  43;  this  latter  figure 
repesents  the  effective  surface  tension  of  water 
modified  by  oil  as  used  in  flotation. 

If  surface  energy  is  freed  in  any  way  it  is 
changed  into  other  forms  of  energy,  especially 
heat,  the  surface  of  the  system  decreasing  at  the 
same  time.  Conversely,  if  heat  is  introduced  into 
a  system  capable  of  developing  free  surface  energy 
the  surface  tension  is  decreased.  Roughly,  the 
decrease  in  surface  tension  is  proportional  to  the 
increase  in  temperature.  Place  powdered  sulphur 

1  "  Soap  Bubbles,"  by  C.  V.  Boys. 

2  Clerk  Maxwell  in  Encyclopedia  Britannica,   under 
Capillarity. 

3  "The  Surface  Tension  of  Water,   Alcohols,   etc.," 
Jr.  of  Am.  Chem.  Soc.y  July,  1915. 

4  "  A  Textbook  of  Physics,"  by  J.  H.  Poynting  and  J.  J. 
Thomson,  1913. 


26  THE  THEORY  OF  FLOTATION 

on  the  surface  of  the  water  on  a  horizontal  plate 
of  clean  metal;  apply  heat  locally;  the  sulphur  is 
pulled  away  by  the  cold  liquid  as  against  the 
feebler  tension  of  the  warmer  liquid.  If  an 
electric  surface  is  produced,  in  that  two  phases 
having  different  electric  charges  which  are  not 
permitted  to  neutralize  each  other  are  brought 
in  contact  with  each  other,  the  surface  tension 
of  the  phase  decreases.1  Further,  the  value  of  a 
surface  tension  varies  with  the  chemical  charac- 
ter of  the  phases  which  are  in  contact  with  each 
other. 

The  elastic  force  at  the  surface  of  a  liquid  tends 
to  draw  it  into  the  most  compact  form.  That  is 
why  drops  assume  the  form  of  a  sphere.  Let 
alcohol  be  added  to  water  until  a  solution  is 
obtained  in  which  a  drop  of  common  lubricating 
oil  will  float  at  any  depth.  Then  with  a  pipette 
insert  a  large  globule  of  oil  beneath  the  surface. 
The  oil  will  be  seen  to  float  as  a  perfect  sphere 
within  the  body  of  the  liquid  2  (Fig.  3). 


FIG.  3. 

The  reason  that  liquids  are  not  more  com- 
monly observed  to  take  the  spherical  form  is 
that  ordinarily  the  force  of  gravity  is  so  great 

1  "Handbook    of    Colloid    Chemistry,"    by   Ostwald 
Fischer. 

2  "A  First  Course  in  Physics,"  by  Millikan  and  Gale. 


as  to  be  more  influential  in  determining  their 
shape  than  are  the  cohesive  forces. 

Water  has  the  highest  surface  tension  of  any 
common  liquid  except  mercury,  so  that  the  ad- 
dition of  another  liquid  usually  lowers  its  sur- 
face tension.  When  the  water  is  modified  by 
oil,  the  contractile  force  of  surface  tension  is 
diminished,  the  bubbles  are  less  fragile,  and 
they  survive  long  enough  to  perform  their  metal- 
lurgical duty  of  buoying  the  metal  particles  to 
the  surface  of  the  liquid  pulp.1  In  practice  the 
modification  of  water  is  effected  by  minute  sub- 
divisions of  an  insoluble  oil,  or  it  may  be  done 
by  means  of  a  soluble  oil  or  derivative,  such  as 
creosol  and  amyl  acetate.  The  surface  tension 
of  a  colloid  solution  at  its  free  surface  may  be 
more,  or  less,  or  equal  to  that  of  the  pure  dis- 
persion medium.  The  surface  tension  of  water, 
while  generally  decreased  by  a  contaminant,  is 
increased  by  gum  arabic,  starch,  and  plum  gum. 
Both  the  increase  and  decrease  in  surface  tension 
,  follows  the  concentration  of  the  colloid.  Traces 
of  fatty  acids,  soaps,  resins,  tannic  acid,  etc., 
suffice  to  greatly  lower  the  surface  tension  of 
water.2 

The  surface  tension  of  colloid  solutions,  as  of 
liquids  in  general,  decrease  as  the  temperature 
rises,  but  is  more  marked  than  in  the  case  of 
the  pure  dispersion  medium  alone.  Coarse  sus- 
pensions and  suspensoids  hardly  alter  the  sur- 


"The  Flotation  Process,"  by  T.  A.  Rickard. 
"H 
Fischer. 


2  ''Handbook    of    Colloid    Chemistry, "    by   Ostwald 


28  THE  THEORY  OF  FLOTATION 

face  tension  of  the  dispersion  medium.1  L. 
Zlobicki  found  coarse  aqueous  suspensions  of 
emery,  mastic,  and  gamboge  and  colloid  sus- 
pensions of  silver  and  platinum  to  have  the 
same  surface  tension  as  the  pure  dispersion 
medium.  The  temperature  coefficient  of  the 
surface  tension  of  these  systems  was  also  the 
same  as  that  of  the  pure  dispersion  means. 
These  results  seem  to  show  that  only  emulsoids 
(colloids  in  the  phase  liquid-liquid)  decrease 
the  surface  tension  of  their  dispersion  media. 

Sodium  hydroxide  affects  greatly  the  surface 
tension  of  soap  solution. 

Oil  serves  as  a  contaminant  that  lowers  the 
surface  tension  of  water,  also  it  augments  the 
viscosity  of  the  liquid.  These  two  effects  unite 
in  facilitating  the  formation  of  strong  and  per- 
sistent froth. 


The  Contact  Angle 

Definition.  —  It  can  easily  be  shown,  as  we 
know  from  flotation  practice,  that  films  of  vari- 
ous kinds  on  particles  either  produce  or  prevent 
flotation.  A  clean  copper  wire  floats,  if  the  sur- 
face is  oxidized  it  sinks  promptly,  while  if  the 
oxide  film  is  changed  to  one  of  sulphide,  the  wire 
again  floats. 

The  reason  for  the  different  behavior  of  these 
three  wires  is  that  the  different  films  result  in 
different  "  contact  angles/'  The  contact  angle 

1  "Handbook  of  Colloid  Chemistry,"  by  Ostwald 
Fischer. 


CONTACT  ANGLE  IN   FLOTATION 


29 


is  the  measure  of  "  wetness  "  or  "  non-wetness  " 
and  is  shown  in  Fig.  4. 


FIG.  4. 

Contact  Angle  in  Flotation.  —  Valentine  has 
proved  theoretically  and  by  practical  tests  that 
one  of  the  flotation  factors  is  the  contact  angle, 
which  must  be  of  a  certain  degree  to  make  flo- 
tation possible,  and  we  can,  therefore,  say  that 
surface  films  either  produce  or  prevent  flo- 
tation, according  to  the  contact  angle. 

We  have  been  talking  of  coatings  that  are 
solid  films,  but  we  can  show  that  a  film  may  be 
either  a  solid,  a  liquid,  a  gas,  or  an  electric 
charge.  The  use  of  oil  in  practice  illustrates  a 
liquid  film,  and  just  as  with  the  solid  film  (oxide, 
sulphide,  metal)  these  liquid  films  will  either 
produce  or  prevent  flotation  according  to  the 
resulting  contact  angle.  Malachite  particles  hav- 
ing a  film  of  sulphide  produced  by  the  action  of 
H2S  floats  very  well;  they  do  so  by  the  contact 
angle  caused  by  the  strongly  adhering  film  of  gas. 

The  following  quoted  from  Taggart  and  Beach 
is  very  interesting.1 

1  "An  Explanation  of  the  Flotation  Process,"  Bull. 
A.I.M.E.,  August,  1916. 


30  THE  THEORY  OF  FLOTATION 

When,  as  is  the  common  case  in  the  flotation 
process,  there  are  three  substances  in  contact, 
a  system  of  forces,  as  shown  in  Fig.  5,  is  brought 


FIG.  5. 

into  play.  If  0  does  not  move  indefinitely  to 
the  right  or  to  the  left,  equilibrium  will  be 
attained  when 

TSL  = 
or  cos0  = 


TGL 

where  TGSj  TGL,  and  TSL  are  the  interfacial  ten- 
sions or  pressure  at  the  gas-solid,  gas-liquid,  and 
solid-liquid  contact  respectively.  From  this 
equation  is  deduced  the  important  conclusion 
that  as  TSL  increases  with  respect  to  TGs,  the 
angle  of  contact  6  becomes  smaller  (the  gas  and 
liquid  being  the  same),  or,  in  other  words,  the 
angle  of  contact  is  a  measure  of  the  tendency 
of  one  fluid  to  replace  another  on  the  surface  of 
a  colloid.  We  have  examined  the  angles  of 
contact  of  the  water-air,  oil-air,  and  oil-water 
surfaces  against  a  number  of  the  common 
minerals.  We  have  found,  in  general,  that  the 
air-water  contact  angle  is  less  for  gangue  minerals 
than  for  sulphide  minerals,  that  the  air-oil  con- 
tact angle  is  less  for  sulphides  than  for  gangues 
and  less  for  any  given  sulphides  than  the  air- 
water  contact  angle,  and  that  the  water-oil  con- 
tact with  solids  takes  the  form  shown  in  Fig.  6. 


CONTACT  ANGLE  IN  FLOTATION 


31 


We  found  further  that  the  invariable  effect 
of  oiling  a  solid  surface  is  to  reduce  the  air- 
water  contact  angles.  This  latter  phenomenon 


FIG.  6. 


is  undoubtedly  aided  by  the  reduction  of  the 
surface  tension  of  the  water  due  to  contamina- 
tion by  the  oil,  The  conclusions  forced  by  ob- 
servation of  the  above  phenomena  are: 

1.  That   water   has   a   smaller   tendency  to 
displace  air  on  the  surface  of  sulphide  minerals 
than  on  the  surface  of  gangue  minerals. 

2.  That  the  tendency  of  oil  to  displace  air  is 
greater  on  the  surface  of  sulphide  minerals  than 
at  the  surface  of  gangue  minerals. 

3.  That  oil  tends  to  displace  water  on  the 
surface  of  sulphides  and  that  water  tends  to 
displace  oil  at  the  surface  of  gangue  minerals. 

4.  That  water  displaces  air  more  readily  on 
an  oil-solid  surface  than  on  a  clean  surface  of 
ths  same  solid. 

5.  That   these   tendencies   toward    displace- 
ment are  due  to  the  interfacial  tensions  or  pres- 
sures existing  between  the  various  substances, 
and  that  the  resulting  action  of  these  interfacial 
forces  is  a  manifestation  of  the  tendency  toward 
reduction  of  the  total  potential  energy  of  the 
system.     Wherever  an  increase  in  the  solid-fluid 
interface  will  decrease  the  potential  energy,  such 
a  change  will  occur. 


32  THE  THEORY  OF  FLOTATION 

It  can  also  be  shown  experimentally  that  an 
electric  charge  will  so  modify  the  contact  angle 
on  a  particle  as  to  permit  flotation  that  would 
otherwise  not  take  place.  A  change  of  potential 
at  the  surface  of  separation  of  a  solid  and  liquid 
will  produce  a  change  of  surface  tension  and 
contact  angle,  and  conversely  a  change  in  sur- 
face tension  by  any  other  means  will  produce  a 
difference  of  potential.1 

A  particle  heavier  than  water  may  be  made  to 
float  provided  it  is  small  enough,  of  proper  shape 
with  respect  to  size  and  weight,  and  provided 
it  has  a  surface  film  the  resultant  of  which  is 
a  contact  angle  that  permits  flotation.  Such 
films  may  be  either  solid,  liquid,  gaseous,  or 
electric  or  a  combination  of  any  of  these. 

This  statement  is  very  near  that  for  the  con- 
ditions required  to  produce  a  colloid  solution  or 
suspension  and  it  is,  therefore,  reasonable  to 
look  to  the  subject  of  colloids  and  of  electro- 
statics, with  which  this  is  closely  connected,  to 
furnish  the  real  reason  for  flotation. 

An  absolutely  clean  particle  free  from  films  of 
any  kind  (which  is  practically  impossible)  will 
not  float;  therefore,  we  can  have  no  flotation 
without  a  surface  film.  While  it  is  a  fact  that 
certain  films  produce  flotation  by  reason  of 
their  contact  angle,  how  do  we  account  for  the 
fact  that  these  films  produce  the  contact  angle 
they  do?-  If  some  mineral  particles  whose  con- 
tact with  water  renders  them  non-wet  are  put 

1  "How  Flotation  Works,"  by  G.  D.  Van  Arsdale, 
Eng.  &  Min.  Jr.,  May  13,  1916. 


CONTACT  ANGLE  IN  FLOTATION    33 

into  the  bottom  of  a  vessel  containing  pure  water 
and  a  bubble  of  air  is  brought  into  contact  with 
this  particle,  they  will  become  attached  and  the 
particle  will  be  carried  up  to  the  surface  with 
the  bubble.  This  goes  to  show  that  it  is  not 
necessary  to  form  the  bubble  in  solution  nor  is 
it  necessary  to  have  nascent  bubbles.1  The 
mere  attachment  of  the  mineral  to  the  bubble, 
or  the  simple  contact  of  gas  and  liquid  surface, 
is  all  that  is  necessary.  In  explaining  why  the 
bubbles  attach  themselves  to  the  mineral  and 
not  to  the  gangue,  the  accompanying  sketch 
represents  a  large  magnified  diagram  of  a  bubble 
of  air  or  gas  in  contact  with  the  two  particles, 
one  of  the  particles  having  assumed  a  contact 

Partical  with  Film  Resulting  Partical  -with  Film  Resulting 

In  "Wet"  Contact  Angle        I  /in  "Non-Wet"  Contact  Angle 


FIG.  7. 

angle  that  would  enable  it  to  float  on  a  watery 
surface,  the  other  particle  having  a  contact 
angle  that  would  produce  immediate  sinking 
on  a  water  surface  (Fig.  7).  Considering  this 
diagram,  it  will  be  seen  that  the  bubble  is  really 
only  the  surface  of  water  in  contact  with  air  or 
gas,  and  that  the  particles  float  on  the  surface 
for  exactly  the  same  reason  as  they  do  in  the 
Macquisten  tube. 

1  "Why  is  Flotation?"  by  Chas.  T.  Durell,  Min.  & 
Sci.  Press,  September  18,  1915. 


34 


THE  THEORY  OF  FLOTATION 


Capillary  Attraction  . 

Capillary  Phenomena.  —  A  study  of  capil- 
larity is  of  great  aid  in  gaining  a  conception  of 
the  conduct  of  the  molecular  forces  of  cohesion 
and  adhesion  that  cause  some  substances  to 
float  on  the  surface  of  a  liquid  while  others  sink.1 
We  must  keep  in  mind  two  familiar  facts: 
First  that  the  surface  of  a  body  of  water  at  rest, 
for  example  a  pond,  is  at  right  angles  to  the 
resultant  force,  that  is,  gravity,  which  acts  upon 
it;  second,  that  the  force  of  gravity,  acting  upon 
a  minute  amount  of  liquid,  is  negligible  in  com- 
parison with  its  own  cohe- 
sive force.  Consider,  then, 
a  very  small  body  of  liquid 
close  to  the  point  0,  Fig.  8, 
where  water  is  in  contact 
with  the  wall  of  the  glass 
tube.  Let  the  quantity  of 
liquid  considered  be  so  mi- 
nute that  the  force  of  grav- 
ity acting  upon  it  may  be 
disregarded.  The  force  of  cohesion  of  the  wall  will 
pull  the  liquid  particles  at  0  in  the  direction  of  0  E. 
The  force  of  cohesion  of  the  liquid  will  pull  this 
same  particle  in  the  direction  OF.  The  result- 
ant of  these  two  pulls  on  the  liquid  at  0  will  then 
be  represented  by  OR,  Fig.  8.  If,  then,  the 
adhesive  force  OE  exceeds  the  cohesive  force 
OF,  the  direction  of  OR  of  the  resultant  force  will 
lie  to  the  left  of  the  vertical  OM ,  Fig.  9,  in  which 
1  "Molecular  Forces  and  Flotation,"  by  Will  H.  Cog- 
hill,  Min.  &  Sci.  Press,  September  2,  1916. 


FIG.  8 


CAPILLARY  PHENOMENA 


35 


case,  since  the  surface  of  the  liquid  always  as- 
sumes a  position  at  right  angles  to  the  resultant 
force,  it  must  rise  up  against  the  wall  as  water 
does  against  glass.  If  the  cohesive  force  OF 
(Fig.  10)  is  strong  in  comparison  with  the  ad- 
hesive force  OE  the  resultant  OR  will  fall  to  the 
right  of  the  vertical,  in  which  case  the  liquid 
must  be  depressed  about  0.  Whether,  then,  a 
liquid  will  rise  against  a  solid  wall  or  be  depressed 


FIG.  9. 


FIG.  10. 


by  it  will  depend  only  on  the  relative  strength  of 
the  adhesion  of  the  wall  for  the  liquid,  and  the 
cohesion  of  the  liquid  for  itself.  Since  mercury 
does  not  wet  glass  1  we  know  that  cohesion  is 
here  relatively  strong,  and  we  should  expect, 
therefore,  that  mercury  would  be  depressed,  as 
indeed  we  find  it  to  be.  The  fact  that  water  will 
wet  glass  indicates  that  in  this  case  adhesion 
is  relatively  strong,  and  hence  we  should  ex- 
pect water  to  rise  against  the  wall  of  the  con- 
taining vessel,  as  in  fact  it  does.  As  soon  as  the 

1  It  is  a  well-known  fact  that  there  is  a  slight  force 
between  mercury  and  glass  and  that  mercury  exerts  an 
attractive  force  upon  air,  but  the  quotation  suffices  for 
the  present. 


36 


THE  THEORY  OF  FLOTATION 


curvatures  just  mentioned  are  produced,  the 
concave  surface  aob  (Fig.  11)  tends,  by  virtue  of 
surface  tension,  to  strengthen  out  into  a  flat  sur- 
face ao1?),  but  it  no  sooner  begins  to  straighten 
than  adhesion  again  elevates  it  at  the  edges. 
It  will  be  seen,  therefore,  that  the  liquid  must 
continue  to  rise  in  the  tube  until  the  weight  of  the 


FIG.  11. 


FIG.  12. 


volume  lifted  balances  the  tendency  of  the  sur- 
face to  flatten  out.  Similarly  a  convex  surface 
aob  (Fig.  12)  falls  until  the  upward  pressure  at 
0  (which  is  small)  balances  the  tendency  of  the 
surface  aob  to  flatten  out.  If,  in  the  case  of 
water  against  glass,  the  water  is  pulled  upward 
and  in  the  case  of  mercury  against  glass  the  mer- 
cury is  pulled  downward,  the  converse  must  also 
be  true,  namely,  that  in  the  former  the  glass  is 
pulled  down  and  in  the  latter  the  glass  is  pulled 
up. 

Result  of  the  Capillary  Attraction.  —  Now 
assume  that  you  had  two  minerals  so  that  they 
are  partly  submerged  by  a  liquid  and  that  with 
one  adhesion  is  very  great  (relatively)  and  that 
with  the  other  adhesion  is  very  slight.  It  is 
obvious  that  the  surface  of  the  liquid  will  turn 


OSMOSIS  37 

up  at  the  contact  with  the  former  and  down 
and  around  the  other,  and  that  if  these  particles 
are  so  small  that  the  force  of  gravity  is  negli- 
gible it  is  impossible  for  the  former  to  float 
and  just  as  impossible  for  the  latter  to  sink. 
One  of  them  cannot  ride  on  the  surface  and  is 
actually  drawn  down  into  the  liquid  like  gold 
into  mercury,  while  the  other  cannot  by  any 
means  enter  the  liquid  unless  its  mass  is  sufficient 
to  overcome  the  contractile  force  in  the  sur- 
face of  the  depressed  liquid.1 

Osmosis 

Definition.  —  When  two  liquids  are  separated 
by  a  porous  membrane,  each  may  pass  through 
the  membrane  into  the  other  with  more  or  less 
freedom;  this  process  is  called  "  osmose."2 

Osmotic  phenomena  connected  with  osmosis 
is  closely  connected  with  the  process  of  diffusion 
and  dialysis.  In  fact,  during  dialysis  the  in- 
crease in  volume  in  the  dialyzing  liquid  in  the 
interior  of  the  cell  is  a  phenomenon  of  osmosis. 

Osmotic  phenomena  takes  place  whenever  a 
dispersoid  is  brought  in  contact  with  the  less 
concentrated  one  or  its  pure  dispersion  means, 
under  conditions  which  do  not  allow  of  free 
diffusion.  This  may  be  accomplished  by  placing 
between  them  a  so-called  semipermeable  or, 
better  expressed,  a  selectively  permeable  mem- 
brane, in  other  words,  a  device  which  gives  pas- 

1  "  Molecular  Forces  and  Flotation, "by  Will.  H.  Coghill, 
Min.  &  Sci.  Press,  September  2,  1916. 

2  "  Essentials  of  Physics,"  by  Hoadley,  p.  127. 


38  THE  THEORY  OF  FLOTATION 

sage  to  the  dispersion  means,  but  not  the  dis- 
persed phase.  These  devices  are  nothing  more 
than  such  as  are  used  in  the  dialysis  of  colloid 
systems.  In  fact,  osmotic  phenomena  may  al- 
ways be  expected  to  appear  during  dialysis  (sub- 
stances which  do  not  dialyze,  or  pass  through 
parchment  paper,  Graham  called  colloids;  those 
which  do,  molecular  dispersoids) .  Osmosis,  like 
free  diffusion,  tends  toward  the  establishment 
of  a  uniform  spatial  distribution  of  dispersed 
phase  and  dispersion  means. 

The  intensity  of  the  tendency  to  bring  about 
a  uniform  distribution  of  dispersed  phase  and 
dispersion  means  may  be  measured  by  opposing 
this  osmotic  leveling  process  by  the  hydrostatic 
pressure  of  a  water  column.  The  pressure  thus 
made  evident  is  called  the  "  osmotic  pressure  " 
of  the  dispersoid. 

Colloids  and  Osmosis.  —  Colloids  tend  to 
concentrate  electrolytes  upon  themselves  and 
thereby  to  increase  the  possibility  of  developing 
and  exhibiting  a  greater  osmotic  pressure  than 
is  really  due  to  colloids  themselves.1  This  in- 
creased osmotic  pressure  would  tend  to  drive  the 
air  from  the  metallic  particles  leaving  them  in 
the  same  condition  as  those  of  the  gangue.  A 
proper  strength  will  sometimes  "  kill "  the 
float,  probably  due  to  the  above  reason. 
However,  colloidal  impurities,  like  tannin, 
saponin,  etc.,  or  volatile  oils  and  the  like,  destroy 

1  The  difficulty  of  " washing  out"  the  last  traces  of 
electrolytes  from  precipitates  is  one  fact  leading  to  this 
conclusion. 


VISCOSITY  39 

bubbles  by  reducing  the  surface  tension,  so  that 
the  gas  pressure  bursts  them.  This  weakening 
of  the  surface  tension  by  a  colloid  is  thus  seen 
to  be  entirely  different  from  the  strengthening  of 
osmotic  pressure  by  a  crystalloid  (molecular 
dispersoid)  although  the  result  is  practically  the 
same  —  no  froth. 

The  osmotic  pressure  of  molecular  dispersoids 
is  governed  by  the  important  law  of  Pfeffer  and 
van't  Hoff :  the  "  osmotic  pressure  is  directly 
proportional  to  the  concentration."  The  rela- 
tions in  colloid  systems  are  not  so  simple. 
Examples  are  known  where  the  law  holds  ap- 
proximately but  there  are  also  those  in  which 
the  "  osmotic  pressure  increases  faster  than  the 
concentration;  or  more  slowly  than  this." 

The  Influence  of  Added  Substances  upon 
Osmotic  Pressure.  —  The  influence  of  added 
substances  upon  the  osmotic  pressure  of  a  given 
system,  that  is,  molecularly  dispersed  solution, 
is  purely  additive.1  In  other  words,  the  pressure 
exerted  by  added  substances  is  added  to  that 
of  the  original  system.  The  effect  of  added 
substances  on  the  osmotic  pressure  of  colloid 
systems  is  more  complicated.  Concentration 
and  temperature  functions  are  encountered. 

Acids  or  alkalis  may  either  increase  or  de- 
crease the  osmotic  pressure  of  different  colloids. 

Viscosity 

A  marked  increase  in  the  viscosity  of  inter- 
facial  films  is  produced  by  the  presence  of  finely- 
1  There  are  exceptions  to  this  rule. 


40 


THE   THEORY  OF  FLOTATION 


divided  solid  matter.  This  increase  can  be 
shown  experimentally 2  by  pouring  any  clear  oil, 
kerosene,  liquid  vaseline,  etc.,  on  to  water  and 
then  bubbling  gas  through  the  water  (Fig.  13). 
The  interface  has  all  the  appearance  of  an  elec- 
tric film.  .Bubbles  rising  through  the  water 
and  striking  the  underside  of  the  interface 
stretch  the  film  H  (Fig.  13)  and  rising  further 
drag  away  a  mass  of  water  surrounded  by  this 
viscous  layer.  The  system  now  appears  as 
shown  at  M  and  rises  to  the  oil-air  surface  on 
account  of  its  lower  specific  gravity.  Here  the 
film,  together  with  the  excess  of  water  carried 
up  as  shown  at  (7,  breaks  away  and  falls  back 
through  the  oil,  not  in  spherical  form,  as  would 


FIG.  13. 

be  the  case  were  the  water  drop  not  surrounded 
by  a  viscous  film,  but  in  hemispherical  form 
(see  P,  Fig.  13)  often  trailing  behind  it  a  film 
with  ragged  edges  as  it  broke  from  the  bubble. 
The  tadpole-shaped  water  drops  H  (Fig.  13) 


VISCOSITY  41 

are  further  evidence  of  the  high  viscosity  of  the 
oil-water  interfacial  film. 

Also  if  finely-powdered  sulphide  is  thrown  in- 
to the  oil  and  allowed  to  settle  to  the  interface, 
it  will  become  entangled  in  the  film;  this  in- 
creased viscosity  is  apparent.  If  now  gas 
bubbles  are  introduced,  as  before,  the  return 
water  drops,  coated  with  a  film  containing  the 
solid  particle,  are  much  more  irregular  in  shape 
than  previously,  and  their  coalescence  after 
reaching  the  interface  requires  days  or  weeks.1 
An  even  more  convincing  proof  of  the  increase 
in  viscosity  of  an  interfacial  film  is  given  by  the 
following  experiment.  If  a  needle  is  floated  at 
the  center  of  a  surface  of  pure  water  in  a  beaker 
4  inches  in  diameter  and  a  chip  of  wood  is 
floated  near  the  wall  of  the  beaker,  the  needle 
may  be  caused  to  revolve  by  means  of  a  magnet 
without  disturbing  the  chip.  If  the  surface  of 
the  water  is  dusted  over  with  fine  ore,  the  whole 
surface  together  with  the  chip  moves  as  though 
it  were  a  rigid  solid.2 

When  gas  bubbles  are  introduced  into  a  liquid 
pulp  where  oil  is  present  there  is  formed  about 
each  bubble  a  liquid  film  whose  surface  tension  is 
less  and  whose  viscosity  is  greater  than  that  of 
the  bulk  of  the  liquid.  Some  of  the  solid  par- 
ticles of  the  pulp  move  into  the  film  and  are 
raised  to  the  surface  with  the  bubble.  Since 

1  "An  Explanation  of  the  Flotation  Process,"  by  Tag- 
gart  and  Beach,  Bull.  A.I.M.E.,  August,  1916. 

2  "An   Explanation    of    the   Flotation    Process,"    by 
Taggart  and  Beach,  Bull.  A.I.M.E.,  August,  1916. 


42  THE  THEORY  OF  FLOTATION 

there  is  a  concentration  of  oil  in  the  film,  and 
since  the  diminution  in  potential  energy  at  an 
oil-sulphide  contact  is  greater  than  at  a  water- 
sulphide  contact,  the  contaminated  layer  re- 
places the  water  on  the  sulphide  and  the 
sulphide  moves  into  the  bubble  film,  while  the 
gangue,  on  which  water  displaces  oil,  remains 
in  greater  measure  in  the  body  of  the  pulp. 
The  bubbles,  therefore,  as  they  arrive  at  the 
surface,  carry  an  excess  of  the  sulphide  minerals. 
Upon  their  arrival  at  the  surface,  the  bubbles 
of  the  contaminated  liquid  persist,  owing:  (1) 
to  their  low  surface  tension;  (2)  to  their  ability 
to  adjust  this  tension  to  a  state  of  stable  equi- 
librium; and  (3)  to  their  greater  viscosity  which 
is  markedly  increased  by  the  presence  of  the 
solid  particles. 

The  following  are  some  of  the  characteristics 
of  molecular  dispersoids: 

1.  When  a  solid  goes  into  solution  the  vis- 
cosity of  the  dispersing  medium  is  usually  in- 
creased;  dilute  solutions  of  some  salts,  such  as 
lithium,  chloride,  and  potassium  chloride,  form 
exceptions  to  this  rule. 

2.  In  normal  cases  the  viscosity  increases  pro- 
gressively with  concentration. 

3.  When   gases   are   dissolved   in   a   solvent 
they  do  not  seem  to  change  its  viscosity. 

Manifold  and  complicated  conditions  arise 
when  two  liquids  are  molecularly  dissolved  in 
each  other.  Thus,  the  mixture  of  alcohol  with 
water  shows  a  characteristic  behavior  in  that 
the  maximum  of  viscosity  is  obtained  in  medium 


VISCOSITY  43 

concentrations  of  the  one  in  the  other,  the  value 
of  which  is  considerably  greater  than  that  of 
pure  compounds. 

It  may  be  regarded  as  typical  of  suspensoids 
that  their  viscosity  is  but  slightly  greater  than 
that  of  their  pure  dispersing  mediums.1  Tem- 
perature affects  the  viscosity  of  the  suspensoids 
in  the  same  way  as  it  does  that  of  normal  li- 
quids: the  viscosity  decreases  with  increasing 
temperature.  Also  according  to  H.  W.  Waustra 
the  condition  of  electrolytes  influences  the  vis- 
cosity of  a  suspensoid  silver  hydrosol  (and  prob- 
ably that  of  all  others)  in  a  very  characteristic 
manner.  The  addition  of  an  electrolyte  de- 
creases the  viscosity;  this  decrease  takes  time, 
occurring  in  some  instances  only  after  days,  and 
it  is  associated  with  a  change  in  the  state  of  a 
colloid,  namely,  with  its  coagulation. 

The  electric  charge  on  suspended  particles 
allow  another  possible  explanation  of  flotation 
phenomena.  Quartz  particles  when  suspended 
in  water  are  negatively  charged;  pyrite  particles 
positively  charged;  oil  drops  are  negatively 
charged,  and  air  bubbles  negatively  charged. 
The  charges  are  somewhat  small  compared  with 
the  weight  of  the  particles,  so  they  are  hardly 
strong  enough  to  cause  negatively-charged 
quartz  to  stick  to  positively-charged  pyrite,  as 
they  can  have  only  a  few  points  of  contact,  and 
currents  in  water  could  easily  pull  them  apart. 
However,  the  negatively-charged  droplet  of  oil, 

1  It  must  be  remembered,  however,  that  this  is  true 
only  when  such  systems  are  dilute. 


44  THE  THEORY  OF  FLOTATION 

which  is  repelled  from  a  negatively-charged 
particle  of  quartz,  can  wrap  itself  around  the 
positively-charged  pyrite  particle  so  that  they 
will  stick  together,  and  the  same  applies  to  air 
bubbles.  The  other  sulphides  known  to  be 
flotative  have  positive  charges  when  suspended 
in  water  or  can  be  made  to  assume  positive 
charges  by  use  of  the  proper  amount  of  proper 
electrolyte.  The  large  effect  of  a  small  amount 
of  sulphuric  acid  on  the  condition  of  flotation 
does  not  seem  at  all  strange  in  this  light. 

The  above  is  O.  C.  Ralston's  theory,  the  logic 
of  which  is  supported  by  Mr.  Callow. 

Adsorption 

Explanation  of  the  Term.  —  The  surface  layer 
between  two  physical  phases  is  the  seat  of  con- 
ditions of  density  and  viscosity,  also  of  apparent 
forces  and  energy  manifestations,  which  are 
notably  different  from  those  in  the  bulk  of 
either  phase.  On  philosophical  grounds  it  is 
impossible  to  consider  that  a  real  physical  dis- 
continuity occurs  at  the  boundary  between  two 
media.  In  other  words,  there  must  be  a  very 
thin  layer  of  transition  in  which  there  is  a  rapid 
but  continuous  change  in  the  concentration  of 
the  components.  This  change  in  the  concentra- 
tion of  a  component  at  the  interface  is  called 
adsorption,  and  may  occur  even  between  two 
phases  which  are  ordinarily  regarded  as  im- 
miscible.1 

1  "An  Explanation  of  the  Flotation  Process,"  by  Tag- 
gart  and  Beach,  Bull.  A.I.M.E.,  August,  1916. 


ADSORPTION  IN  FLOTATION  45 

.  The  terms  adsorption  and  absorption  have 
been  used  interchangeably  in  some  writings, 
thus  contributing  to  the  already  existing  con- 
fusion of  ideas. 

Adsorption  in  Flotation.  —  The  question  of 
adsorption  undoubtedly  plays  an  important  part 
in  flotation,  since  it  is  so  requisite  to  the  pro- 
duction of  a  variable  surface  tension.  There 
can  be,  of  course,  no  surface  tension  without 
adsorption,  which  produces,  in  the  case  of 
positive  adsorption,  an  increased  surface  con- 
centration resulting  from  a  lowering  of  the  sur- 
face tension  by  contaminating  and  dissolved 
substances,  whatever  they  may  be.  The  equa- 
tion of  Gibbs  u  =  —  -7^  •  ~r  gives  the  relation- 
jKt  dc 

ship  between  surface  tension  and  the  distribution 
of  the  solute  between  the  bulk  of  the  liquid  inter- 
face. Here  the  notation  is 

u  =  excess  of  substance  in  the  surface  layer, 

c  =  concentration  in  the  main  body  of  the 

liquid, 
R  =  the  gas  constant, 

t  =  absolute  temperature, 

o  =  surface  tension. 

This  shows  that  when  the  surface  tension  is  re- 
duced by  the  addition  of  a  contaminant  the 

quantity  -7-  is  negative  and  "  -^  "   is   positive 
dc  kvv 

(from  algebraic  considerations).  The  surface 
film,  then,  contains  more  of  the  contaminant 
than  the  main  body  of  the  solution.  If  the 
surface  film  contains  less  of  the  contaminant 


46  THE   THEORY  OF  FLOTATION 

than  the  main  body  of  the  solutions  it  is  a 
case  of  "  negative  adsorption/7 

Adsorption  at  a  gas-liquid  interface  may  be 
demonstrated  as  follows:  If  a  solid,  which  has 
been  heated  in  a  vacuum,  is  introduced  into  a 
measured  volume  of  a  gas  over  mercury  in  a 
calibrated  tube,  an  amount  of  the  gas  will  be 
absorbed,  as  is  shown  by  the  change  in  pressure 
and  volume  compared  to  the  space  originally 
occupied.  The  following  additional  facts  are 
stated  by  Taggart  and  Beach:1 

(a)  The  amount  of  gas  adsorbed  at  constant 
temperature  increases  with  the  pressure. 

(6)    It  is  different  for  different  gases. 

(c)  It  is  different  for  different  solids. 

(d)  It  increases  as  the  temperature  decreases. 

(e)  There  is  an  energy  transformation  which  is 
indicated  by  the  heat  development  through  ad- 
sorption. 

(/)  Chemical  reactions  are  assisted  by  the 
adsorbed  layer. 

It  follows  that  the  gas  layers  must  vary  in 
density,  falling  off  rapidly  with  increasing  dis- 
tance from  the  solid.  Quincke  assumes  that 
the  density  of  the  gas  next  to  the  solid  is  equal 
to  that  of  the  solid  and  concludes  that  the 
amount  adsorbed  will  increase  with  the  density 
of  the  solid.  From  these  facts  are  concluded: 

1.  That  gases  and  solids  exhibit  selective  ad- 
hesion and  that,  therefore,  gas  bubbles  will 
attach  themselves  more  persistently  to  some 
substances  than  to  others. 

1  "An  Explanation  of  the  Flotation  Process,"  Bull. 
A.I.M.E.,  August,  1916. 


ADSORPTION  IN  FLOTATION  47 

2.  That  the  selective  adhesion  is  a  manifes- 
tation of  a  definite  amount  of  energy  possessed 
by  each  unit  area  of  a  gas-solid  contact,  and 
that  this  potential  energy  is  capable  of  variation. 

3.  That  chemical   reactions  which   diminish 
this  potential  energy  are  aided  by  adsorption. 

Adsorption  of  the  gas  at  a  gas-liquid  surface  is 
indicated : 

1.  By  the  effect  on  the  surface  tension.     The 
surface    of    a    freshly-formed    mercury   surface 
does  not  change  in  a  vacuum,  but  falls  off  in 
the  presence  of  different  gases  for  about  an  hour. 
Certainly  the  density  of  a  liquid  cannot  be  con- 
stant at  the  boundary  but  must  go  over  con- 
tinuously into  that  of  the  gas. 

2.  By  the  increase  in  the  solvent  power  of  the 
surface. 

3.  In  the  case  of  contaminated  liquids  by 
the  concentration  of  one  or  more  of  the  com- 
ponents of  the  liquid  at  the  gas-liquid  surface. 
Every  unit  area  of  such  a  boundary  possesses 
a  definite  potential  energy  which  always  tends 
to  a  minimum.     If,  therefore,  the  surface  tension 
of  a  solution  depends  upon  the  presence  of  any 
component,  such  a  change  of  concentration  of 
that  component  will  occur  as  will  reduce  the 
potential   energy,   i.e.,   interfacial   tension.     In 
other    words,    any    component    which    reduces 
surface  tension  will  be  found  in  excess  at  the 
surface  of  a  solution. 


48  THE  THEORY  OF  FLOTATION 

Emulsification 

Effect  upon  Flotation.  —  By  some  writers  the 
combination  of  pulp,  oil,  water,  acid,  or  whatever 
other  chemical  substance  is  added,  is  often  re- 
ferred to  as  an  emulsion.  Going  back  to  the 
definition  of  an  emulsion,  we  find  that  it  is  a 
colloid  suspension  of  one  liquid  in  another.  It 
is  true,  that  oil  may  be  so  finely  divided  that  it 
simulates  a  true  emulsion.  If,  as  has  been  said, 
the  colloid  condition  is  antagonistic  to  flotation 
success,  then  the  pulp-oil  combination  is  not  a 
true  emulsion  since  we  clearly  do  get  flotation 
results  from  it.  The  latter  statement  is  true;  it 
is  not  an  emulsion.1 

In  this  connection  G.  D.  Van  Arsdale  states:2 

From  experiment  I  think  it  is  safe  to  say  that 
if  a  particle  meets  emulsified  oil,  there  will  be 
no  attachment  of  oil  to  mineral  unless  some 
factor  is  introduced  that  will  break  up  or  de- 
stroy the  emulsified  condition,  and  that  conse- 
quently emulsification  of  an  oil  should  be  avoided 
in  flotation  practice.  If  this  is  true,  we  would 
expect  that  substances  capable  of  producing 
an  emulsified  condition  of  oils  would  be  harmful 
in  practice,  and  conversely  that  substances 
capable  of  preventing  or  breaking  up  emulsi- 
fication would  be  beneficial.  I  believe  that  this 
is  the  explanation  for  the  puzzling  deleterious 
action  of  some  organic  substances,  such  as  glue, 
tannin,  and  saponin,  since  these  all  belong  to  the 
class  of  compounds  that  are  efficient  and  emulsi- 
fying oils.  Furthermore,  it  is  easy  to  show 

1  "The  Flotation  Process,"  by  Megraw,  p.  30. 

2  "How  Flotation  Works,"   by  G.   D.   Van  Arsdale, 
Eng.  &  Min.  Jr.,  May  13,  1916. 


EMULSIFICATION  49 

experimentally  that  sulphuric  acid  prevents  or 
breaks  up  emulsion  of  oils,  and  it  seems  reason- 
able to  suppose,  therefore,  that  this  is  one  of  the 
reasons,  although  it  may  not  be  the  only  one, 
for  the  use  of  acid.  The  fact  that  acid  is  not 
generally  used  at  present  is  probably  due  to  the 
fact  that  the  oils  and  mixtures  now  in  use  in 
many  places  are  not  such  as  to  emulsify  readily. 

There  are-  a  number  of  other  substances  besides 
sulphuric  acid  having  the  property  of  preventing 
or  destroying  emulsions.  Table  II  shows  the 
relative  efficiency  of  some  of  these  that  have 
been  tested. 

TABLE  II.     EMULSION  MODIFYING  AGENTS. 

Sulphuric  acid 0.244  per  cent  entirely  prevents 

emulsification. 

Cresylic  acid 0 . 006  per  cent  entirely  prevents 

emulsification. 

Acetic  acid 0.014  per  cent  entirely  prevents 

emulsification. 

Citric  acid 0 . 06  per  cent  entirely  prevents 

emulsification. 

Aluminium  sulphate ...  0 . 06  per  cent  prevented  emul- 
sification. 

Copper  sulphate 0 . 30  per  cent  prevented  emul- 
sification. 

Ferrous  sulphate no  action. 

Caustic  soda 0 . 30    per  cent  no  action. 

Sodium  chloride stabilizes  and  increases 

emulsification. 

In  a  case  where  sulphuric  acid  is  used  for 
preventing  emulsification  of  oil,  we  would, 
therefore,  expect  that  the  substances  enumerated 
could  be  substituted  with  equal  effect  in  the 
relative  amounts  indicated  by  the  figures. 


50  THE  THEORY  OF  FLOTATION 

Wilder  D.  Bancroft  has  written  a  series  of 
articles  on  "  The  Theory  of  Emulsification  "  in 
the  Journal  of  Physical  Chemistry,  out  of  which 
very  useful  data  with  regard  to  the  character- 
istics of  an  emulsifying  agent  can  be  obtained. 
His  article  in  the  April  number  of  1915  is  of 
special  interest  as  quite  a  number  of  very  useful 
experiments  are  cited.  He  says:1 

For  a  substance  to  be  an  emulsifying  agent,  it 
must  tend  to  pass  into  the  surface  separating  the 
two  liquids  and  form  a  coherent  film  there. 
If  the  emulsifying  agent  does  not  form  a  co- 
herent film  the  emulsion  will  crack. 

When  two  liquids,  which  are  partially  im- 
miscible, come  together,  we  have  a  surface  that 
separates  these  two  liquid  phases,  and  this  sur- 
face is  called  a  dineric  2  interface.  In  order  to 
fully  understand  the  water-air  interface,  it  may 
be  of  value  to  study  a  case  where  we  have  a 
dineric  interface. 

The  following  extract  from  Wilson's 3  account 
of  an  experiment  which  he  carried  out  as  early 
as  1848  will  serve  the  purpose  as  well  as  any. 

When  chloroform  is  placed  in  a  test-tube,  or 
other  vessel  of  glass,  standing  on  a  horizontal 
surface,  it  exhibits,  like  other  substances  which 
wet  that  solid,  a  curved  surface  with  the  con- 
cavity upwards.  If  water,  or  an  aqueous  solu- 
tion of  nitric,  sulphuric,  or  muriatic  acid,  be 
poured  upon  the  stratum  of  chloroform,  the 
surface  of  the  latter  immediately  changes  the 

1  Bancroft,  Jour.  Phys.  Chem.,  19,  275  (1915). 

2  Bell,  Jour.  Phys.  Chem.,  9,  531  (1905). 

3  Jour.  Chem.  Soc.,'1,  174  (1848). 


EMULSIFICATION  51 

direction  of  its  curve,  and  becomes  convex  up- 
wards, the  convexity  induced  being  much  greater, 
however,  than  the  previous  concavity.  If,  on 
the  other  hand,  an  aqueous  solution  of  potash, 
soda,  or  ammonia  be  placed  above  the  chloro- 
form, the  latter  ceases  at  its  upper  limit  to 
present  a  sensible  curvature  upwards  or  down- 
wards, and  shows  a  surface  which,  to  an  un- 
assisted eye,  appears  to  be  flat.  It  is  to  the 
property  of  an  acid  to  round,  and  of  an  alkali 
to  flatten,  the  surface  of  various  liquids,  of  which 
chloroform  is  one,  that  I  seek  specially  to  direct 
attention. 

The  phenomena  referred  to  cannot  seem  re- 
markable when  merely  described  but  they  have 
appeared  strikingly,  and,  I  may  say,  startling 
to  most  of  those  that  have  witnessed  them. 
They  are  best  observed  by  dropping  into  a 
perfectly  clear,  flat-bottomed  glass  vessel  con- 
taining pure  water,  a  quantity  of  chloroform  too 
small  in  amount  to  touch  the  walls  of  the  vessel 
on  every  side.  The  heavier  liquid  then  shows 
itself  as  a  brilliant,  highly  mobile  globule.  If 
alkali  be  now  added  the  chloroform  in  a  moment 
collapses,  sinks  as  if  exposed  to  a  crushing  force, 
and  flattens  out  on  the  bottom  of  the  glass.  On 
slightly  supersaturating  the  alkali  with  acid, 
the  flattened  chloroform  starts  into  its  previous 
globular  shape  with  a  momentum  and  rapidity 
such  as  might  be  exhibited  by  a  highly  elastic 
substance,  like  a  ball  of  caoutchouc  suddenly 
relieved  from  enormous  pressure.  When  the 
acid  in  its  turn  is  supersaturated  with  alkali, 
and  the  flattening  again  occurs,  by  alternating 
the  addition  of  these  reagents,  the  same  globule 
may  be  successively  flattened  and  rounded  for 
any  number  of  times. 

Change  in  configuration,  however,  is  not  the 
only  alteration  which  the  globule  of  chloroform 
undergoes.  Some  of  the  other  physical  proper- 


52  THE  THEORY  OF  FLOTATION 

ties  are  markedly  altered  by  its  contact  with 
acids  and  alkalis.  These  changes  are  best  seen 
when  a  deep,  white  saucer,  or  flat-bottomed 
porcelain  basin,  is  made  use  of  as  the  containing 
vessel.  When  acidulated  water  is  placed  in  this 
and  chloroform  let  fall  into  it,  the  denser  fluid 
is  scarcely  wetted,  and,  although  nearly  half  as 
heavy  again  as  pure  water,  sinks  reluctantly. 
If  the  drops  indeed  be  small,  they  never  reach 
the  bottom,  but  on  floating  on  the  surface,  evapo- 
rate away.  Those  which  descend  form  globules 
very  mobile  and  readily  obeying  the  solicitation 
of  gravity.  When  separate  globules  melt,  they 
rapidly  flow  together,  and  scarcely  one  is  seen 
without  a  bubble  of  air  attached  to  its  upper 
surface  adhering  tenaciously.  When  the  water, 
on  the  other  hand,  is  an  alkali,  the  chloroform  is 
quickly  wetted  and  sinks  swiftly.  The  drops, 
if  small,  become  circular  discs  with  rounded 
edges;  if  large  they  are  oval,  or  spread  out  into 
elongated,  irregularly  ovoidal,  or  flattened  cylin- 
drical forms.  Their  shape,  however,  is  changed 
by  the  slightest  impulse,  or  inclination  of  the 
containing  vessel  in  a  way  which,  perhaps,  might 
best  be  illustrated  by  comparing  it  to  the  ever- 
varying  elongation,  contractions,  and  irregular 
swellings,  which  alter  the  configuration  of  an 
active  living  leech  in  a  glass  of  water.  The 
flattened  globule,  moreover,  is  much  less  mo- 
bile than  the  rounded  one  in  acid.  The  former 
moves  sluggishly,  even  down  an  inclination, 
clings  to  the  vessel,  and  when  compelled  to  move 
rapidly  leaves  a  tail  behind  it,  like  foul  mercury. 
No  air-bells  attach  themselves  to  it  and  its 
brilliancy  is  sensibly  diminished,  as  if  its  re- 
fractive index  had  altered. 

From  this  experiment  we  can  very  clearly 
see  how  the  dineric  interface  changes  in  shape 
when  an  acid  or  alkali  is  added  to  the  system. 


ELECTRICAL  PHENOMENA  53 

The  interfacial  tension  is  markedly  altered  in 
both  cases.  In  the  flotation  process  the  emul- 
sifying agent  alters,  in  the  same  way,  the  inter- 
facial  tension  existing  between  the  surface  of  the 
water  and  the  air  bubble.  The  result  is  that 
the  metallic  sulphide  particles  find  it  more  diffi- 
cult to  pierce  the  water-air  interface  than  when 
there  is  no  emulsifying  agent  to  make  a  more 
coherent  film.  Thus  the  oil  will  make  it  possible 
for  a  larger  number  of  sulphides  to  adhere  to 
this  usually  spherical  film.1 

Electrical  Phenomena  in  Flotation 

Such  an  authority  as  Thomas  M.  Baines,  Jr., 
states:2 

If  one  turns  to  "  Elementary  Lessons  in  Elec- 
tricity and  Magnetism,"  by  Silvanus  Thompson, 
and  studies  the  fundamental  principles  of 
frictional  electricity,  as  given  in  Chapter  I, 
a  clearer  idea  of  the  causes  of  "  flotation  "  may 
be  obtained.  The  electrical  theory  was  taught 
last  year  as  possibly  explaining  flotation  phe- 
nomena to  the  class  in  ore-dressing,  at  the 
Case  School  of  Applied  Science. 

In  his  article  Mr.  Baines  gives  the  following 
summary  of  requirements  for  "  flotation  "  from 
the  electrical  standpoint: 

1.  Ores  containing  valuable  minerals  or  metals 
that   are   good   conductors   are  the   only   ones 
suitable  for  flotation. 

2.  To  buoy  these  conductors,  it  is  necessary 

1  "  The  Flotation  Process/'  by  Stander. 

2  "  The  Electrical  Theory  of  Flotation,"  by  Thomas  M. 
Baines,  Jr.,  Min.  &  Sci.  Press,  November  27,  1915. 


54  THE  THEORY  OF  FLOTATION 

to  supply  electrified  bubbles  from  below  to  float 
particles  of  the  conductors  that  are  attached; 
hence  the  smaller  the  bubble,  the  better  the 
result,  the  gas  being  the  same. 

3.  Some  dielectric  fluid  is  necessary  to  cover 
the  conductor  of  the  bubbles  to  prevent  the 
dissipation  of  the  electric  charge.     The  thinner 
the  film  of  dielectric  and  the  greater  its  dielec- 
tric strength,  the  greater  the  effective  attractive 
force  and  the  more  permanent  will  be  the  froth. 

4.  Some  material  must  be  added  to  the  water 
to  increase  its  conductivity  to  obtain  a  clean 
concentrate;    acids  in  small  quantities  are  now 
used. 

The  following  experiments  were  conducted 
to  illustrate  electrical  phenomena: 

If  powdered  galena  ore  with  a  limestone 
gangue  be  dropped  into  pure  water,  most  of  the 
powder  will  immediately  sink  to  the  bottom. 
As  the  air  enclosed  by  the  particles  is  expelled 
gradually,  one  sees  the  formation  of"  armored  " 
bubbles,  some  of  which  may  last  for  days. 
Here  is  flotation  without  oil  or  acid.  If  nitric 
acid  is  added,  the  gas  bubbles,  formed  by  the 
action  of  the  acid  on  the  gangue,  will  carry  up 
particles  of  galena,  some  reaching  the  surface 
and  bursting,  while  others  too  heavily  loaded 
with  galena  particles  will  hover  just  below  the 
surface.  These  will  form  clusters,  resembling 
bunches  of  grapes,  and  when  enough  gas  bubbles 
join  the  clusters,  they  start  upwards  toward  the 
surface,  but  generally  before  reaching  there 
they  are  overloaded  by  particles  falling  from 
the  bubbles  that  are  bursting  at  the  surface. 
The  bubbles  with  their  loads  often  resemble 
balloons,  with  the  galena  hanging  onto  the 


ELECTRICAL  PHENOMENA  55 

bottoms,  as  do  the  baskets  of  actual  balloons. 
Some  of  the  bubbles  will  be  completely  "  ar- 
mored "  while  others  will  be  nearly  free  from 
galena.  Another  experiment  that  may  be  suc- 
cessfully used  in  the  laboratory  for  flotation  for 
different  sulphides,  such  as  old  rusty  pyrite 
concentrate,  like  sweeping  from  floors  of  old 
mills,  is  as  follows:  Mix  the  ore  with  bleach- 
ing powder,  some  carbonate  (say,  sodium  car- 
bonate), and  water.  Put  the  mixture  into  a  glass 
beaker  and  add  concentrated  nitric  acid  until 
red  nitrous  fumes  are  given  off.  Chlorine  also 
will  be  evolved.  The  bubbles  of  gas  are  so 
highly  charged  electrically  that  pyrite  from  the 
Mother  Lode  between  10-  and  20-mesh  size  was 
floated,  making  a  complete  separation  from  the 
quartz  gangue.  In  this  experiment  nitrous 
oxide  was  the  active  agent,  for  if  the  same  ex- 
periment is  conducted  with  sulphuric  acid,  no 
such  separation  takes  place. 

Mr.  Baines  accounts  for  the  electrification  of 
bubbles  as  follows: 

(a)  Two  different  substances,  whether  gase- 
ous, liquid,  or  solid,  when  brought  intimately 
into  contact  and  moved  one  over  the  other, 
always  produce  electrification. 

(6)  Difference  of  temperature  of  two  similar 
substances  in  frictional  contact  will  cause  elec- 
trification, the  warmer  usually  being  negatively 
charged. 

(c)  Something  certainly  happens  when  the 
surface  of  two  different  substances  are  brought 
into  intimate  contact,  for  the  result  is  that 
when  they  are  drawn  apart,  they  are  oppositely 
charged.  The  nature  of  the  charge  depends  on 
the  substance.  Fur  rubbed  on  glass  electrifies 


56  THE  THEORY  OF  FLOTATION 

the  glass  negatively;    while  if  glass  is  rubbed 
with  celluloid  it  will  become  positively  charged. 

(d)  A  blow  struck  by  one  substance  on  an- 
other produces  opposite  electrical  states  on  the 
two  surfaces. 

(e)  The    evaporation    of    liquids    is    accom- 
panied by  electrification,  liquid  and  vapor  as- 
suming opposite   charges,   though  this  is  only 
apparent  when  the  surface  is  in  agitation.     A 
few  drops  of  copper  sulphate  thrown  on  a  hot 
platinum  plate  produces  violent  electrification, 
as  the  copper  sulphide  evaporates. 

(/)  Electrical  charges  are  set  up  by  various 
other  means,  such  as  vibration  disruption  of 
material,  crystallization,  combustion,  pressure, 
and  chemical  reactions. 

He  concludes: 

It  would  seem  easier,  therefore,  to  electrify 
a  bubble  than  to  keep  it  from  being  electrified. 
I  assume  that  the  bubbles  are  electrified,  whether 
by  means  of  air  being  forced  through  canvas, 
by  beating  air  into  water  with  paddles,  or  by 
other  means.  So  air  bubbles  that  are  electri- 
fied will  attract  conductors  near  them  that  are 
free  to  move.  Air,  being  a  poor  conductor  of 
electricity,  the  bubbles  as  a  whole  do  not  dis- 
charge immediately  upon  contact  with  a  con- 
ductor. The  only  part  of  the  surface  discharged 
is  that  in  immediate  contact  with  the  conductor, 
and  this  discharged  film  of  air  acts  as  a  di- 
electric and  non-conductor  to  the  rest  of  the 
bubble,  which  remains  charged. 


ELECTRICAL   PHENOMENA  57 

The  above  theory  has  been  tolerated  by  0.  C. 
Ralston l  and  supported  by  J.  M.  Callow.2 
Ralston  states  as  follows: 

The  electric  charges  on  suspended  particles 
allow  another  possible  explanation  of  flotation 
phenomena.  We  find  in  some  of  the  colloid 
chemical  literature  that  quartz  particles  when 
suspended  in  water  are  negatively  charged, 
pyrite  particles  positively  charged,  oil  droplets 
negatively  charged,  and  air  bubbles  negatively 
charged.  The  charges  are  somewhat  small 
compared  with  the  weight  of  the  particles,  so 
that  they  are  hardly  strong  enough  to  cause 
negatively-charged  quartz  to  stick  to  positively- 
charged  pyrite,  as  they  can  have  only  a  few 
points  of  contact,  and  currents  in  water  could 
easily  tear  them  apart.  However,  the  nega- 
tively-charged droplet  of  oil,  which  is  repelled 
from  a  negatively-charged  particle  of  quartz, 
can  wrap  itself  around  the  positively-charged 
pyrite  particles  so  that  they  will  stick  together 
and  the  same  applies  to  air  bubbles.  The 
other  sulphides  known  to  be  flotative  have  posi- 
tive charges  when  suspended  in  water  or  can 
be  made  to  assume  positive  charges  by  the  use 
of  the  proper  amount  of  the  proper  electrolyte. 
So  it  can  be  seen  that  the  application  of  these 
principles  gives  no  difficulty  in  explaining  flo- 
tation from  an  entirely  new  standpoint. 

Callow's  theory  is  stated  briefly  as  follows: 

That  oil  flotation  is  an  electrostatic  process. 
It  is  a  scientific  fact  that  when  a  solid  particle  is 
suspended  in  water  the  water  will  form  around 

1  "Why  Do  Minerals  Float?"  by  O.  C.  Ralston,  Min. 
&  Sci.  Press,  October  23,  1915. 

2  "Notes on  Flotation,"  by  J.  M.  Callow,  Min.  &  Sci. 
Press,  December  4,  1915. 


58  THE  THEORY  OF  FLOTATION 

the  particle  a  contact-film  that  generally  pos- 
sesses an  electric  charge,  the  amount  and  polarity 
of  which  will  depend  upon  the  nature  of  the 
surface  of  the  particle  and  the  electrolyte  in 
which  it  is  suspended.  The  presence  of  these 
charges  can  be  demonstrated  by  the  fact  that 
particles  possessing  them  will  migrate  when 
placed  in  an  electric  field.  It  has  been  dem- 
onstrated that  floatable  particles  have  charges 
of  one  polarity  (positive),  and  that  non-float- 
able particles  have  charges  of  opposite  polarity 
(negative),  and  that  this  froth  is  charged 
negatively  and  so  attracts  the  positively-charged 
or  floatable  minerals,  and  repels  the  negatively- 
charged  or  non-floatable  ones.  It  is  this,  it  is 
believed,  that  causes  the  floatable  minerals, 
such  as  galena  or  sphalerite,  to  adhere  to  the 
froth  and  rise,  while  the  gangue  minerals,  such 
as  silica  and  limestone,  remain  in  the  liquid  where 
they  can  be  discharged  as  tailings. 

C.  T.  Durell  in  his  osmotic  hypothesis  states: 1 

Electricity  may  manifest  itself  in  various 
ways,  but  flotation  cannot  take  place  without 
nascent  or  occluded  gas  and  that,  all  theories 
of  flotation,  be  they  electrical  or  otherwise,  must 
come  to  osmosis  for  their  solution. 

F.  A.  Fahrenwald  conducted  a  series  of  ex- 
periments to  investigate  the  phase  of  the  process 
that  caused  the  bond  between  the  flotative  min- 
eral and  the  bubble  carrier. 

Before  proceeding  to  the  discussion  of  the 
electrical  theory,  he  very  wisely  stated  eight  of 

1  " Flotation  Principles,"  by  C.  T.  Durell,  Min.  &  Sci. 
Press,  February  19,  1916. 


ELECTRICAL  PHENOMENA  59 

the  most  important  fundamental  facts  of  electro- 
statics.    They  are : 1 

A.  The  production  of  electricity  by  friction 
is   a   common    phenomenon;     almost   any   two 
bodies  become  electrified  if  they  are  rubbed  to- 
gether.    In  the  case  of  several  instances,  con- 
siderable force  is  then   necessary  in  order  to 
separate    them.     Attraction    or   repulsion    also 
occurs  when  an  electrified  body  is  brought  near 
bodies  that  have  been  subjected  to  friction,  and 
if  these  are  light  enough  (as -bits  of  pitch,  feathers, 
wood,  paper,  etc.)  they  may  be  lifted.     Bodies 
may  also  become  electrified  by  coming  in  con- 
tact  with   other  bodies   that   already   carry   a 
charge.     In   this   case   the   first   body   receives 
electricity  of  the  same  sign  from  the  charged 
body  and  is  then  repelled. 

B.  Bodies  that  when  electrified  at  one  point 
are  immediately  electrified   all   over  are  called 
good   conductors;  those  over  which  the  charge 
diffuses  slowly  are  poor  conductors.     All  metals, 
many  metallic  ores,  graphite,  ordinary  distilled 
water,  and  aqueous  solutions  of  salts  are  good 
conductors. 

C.  If  a  piece  of  metal,  or  other  conducting 
material  held  in  the  hand  is  rubbed  against  a 
non-conductor  —  say,  a  piece  of  dry  flannel  — 
only  the  non-conductor  appears  afterward  to  be 
electrified.     The    reason    is    that    the    electri- 
fication produced  on  the  metal  spreads  over  the 
hand,  arm,  and  body  of  the  experimenter  to  the 
floor  and  walls  of  the  room.     If,  however,  the 
conductor  is  insulated,  the  degree  of  its  electri- 
fication cannot  be  increased  or  decreased. 

D.  By  whatever  process  a  body  is  electrified 
there  is  always  an  equal  amount  of  electricity 
of  the  opposite  sign,  which  may  reside  upon  the 

1  "The  Electrostatics  of  Flotation,"  by  F.  A.  Fahren- 
wald,  Min.  &  Sci.  Press,  March  11,  1916. 


60  THE  THEORY  OF  FLOTATION 

walls  of  the  enclosing  room  or  upon  some  other 
surface  insulated  from  the  conductor.  Bodies 
carrying  opposite  charges,  when  brought  in 
contact  or  connected  by  a  conductor,  become 
discharged.  If  the  charges  are  equal  they  are 
neutralized,  but  if  one  carries  more  than  the 
other  the  system  takes  on  the  sign  of  the  excess 
charge. 

E.  If  these   bodies   are   strongly   electrified, 
discharge  can  take  place  through  an  appreciable 
thickness  of  non-conducting  material,   such  as 
air,  oil,  or  glass.     This  discharge  is  facilitated 
by  the  presence  of  sharp  projections  upon  either 
body. 

F.  (a)    The  space  between  two  charged  bodies 
is  filled  with  lines  of  force  that  tend  to  move  a 
contained  body  in  the  direction  of  the  local  lines 
of  force  leading  to  the  surface  carrying  the  op- 
posite sign. 

(b)  These  lines  of  force  do  not  penetrate  the 
surface  of  the  conductors  forming  its  boundaries 
and  a  hollow  conductor  is  electrified  on  its 
outside  or  inside  surface  only,  depending  upon 
whether  the  opposite  charge  resides  upon  one 
contained  without  the  sphere  or  upon  one  con- 
tained within  and  insulated  from  the  shell.  In 
the  latter  case  the  entire  field  is  contained  within 
the  inner  surface  of  the  sphere,  and  in  the 
former  case  there  is  no  charge  within  the  hollow 
conductor. 

G.  The    force  .exerted    between    two    small 
charged  bodies  as  given  in  the  equation, 


in  which  q  and  q'  are  the  charges  in  electro- 
static units  carried  by  each  of  the  two  bodies 
and  d  is  the  distance  between  their  centers  of 


ELECTRICAL  PHENOMENA  61 

charge.1  If  the  bodies  are  separated  by  a 
medium  other  than  air  a  factor  Ky  known  as  its 
dielectric  coefficient,  must  be  used  and  the 
equation  becomes 

jF^i.ffl! 

fc"  d*' 

H.  Matter  itself  is  not  acted  upon  by  an  elec- 
tric force,  which  acts  only  between  different 
quantities  of  electricity.  When  a  conductor  is 
introduced  into  an  electric  field  it  represents  a 
gap  or  an  interruption  of  the  lines  of  force, 
resulting  in  an  electrification  of  its  surfaces  only, 
that  part  becoming  positive  which  is  presented 
toward  the  negative  boundary  of  the  field  and 
the  reverse.  In  other  words,  the  original  field 
is  divided  into  two.  This  same  effect  is  produced 
in  the  case  of  a  poor  conductor  but  to  an  ex- 
ceedingly small  degree.  This  explains  the  at- 
traction of  small  bodies  by  another  that  has 
been  electrified  by  friction,  in  which  case  elec- 
trification by  influence  precedes  attraction,  and 
what  is  really  observed  is  attraction  between 
opposite  electric  charges. 

The  following  experiments  were  conducted  by 
Fahrenwald  (see  Fig.  14)  which  should  serve 
to  check  the  various  points,  as  outlined  by  Mr. 
Baines,  as  requirements  for  the  electrical  theory. 

1.  Galena  ore  was  ground  in  an  agate  mortar 
and  poured  from  an  agate  spoon  (to  prevent 
discharge  of  positive  electricity,  if  present,  from 
ore)  between  two  plates  of  an  electrostatic  ma- 
chine. The  material  was  deflected  as  shown. 
Plates  were  electrified  almost  to  discharge 
point.  This  shows  that  galena  ground  under 

1  The  force  by  a  charged  sphere  acts  as  if  originated  at 
the  center. 


62 


THE   THEORY  OF  FLOTATION 


£~ 

—  x 

rJ?n_—  : 

% 

Eo££: 

Q 

_u_u_  : 

i! 

rijc  : 

1 

S&; 

Fig.  1. 


Fig,  4. 


•'''    Vuv\ 

*:  ^ 

o 

:^p: 

'V1' 

o  

-£^- 

'.* 

•  •' 

fe 

rY^'^^t. 

:  o-t-Q-.  : 

Fig.  2. 

-     0-  '_  0    - 

Fig.  5. 


Connecting  Spheres,  connected 
by  conductor  (water) 

FIG.  14. 


Fig.  8. 


ELECTRICAL  PHENOMENA  63 

insulating  conditions  carries  a  charge  and  that 
a  particle  of  this  nature,  suspended  in  a  non- 
conductor in  an  electrostatic  field,  is  attracted. 

2.  Ore   was    ground    in    conducting   earthed 
mortar  and  poured  from  earthed  spoon.     De- 
flection of  only  a  very  few  particles  was  shown. 
Perhaps  the  deflected  particles  were  insulated 
with  oil  or  did  not  come  in  contact  with  earthed 
surface. 

3.  Ore  treated  as  in  No.  1  and  poured  between 
glass  sides  of  a  cell.     Glass  was  1  mm.  thick 
and  separated  by  two  centimeters.     Potential 
between    plates    of    machine    was    8500    volts. 
Deflection    as     shown.     The    interposition    of 
glass  had  very  little  effect. 

4.  As  in  No.  3,  but  the  cell  was  full  of  water. 
Used  conductivity,   tap,   and  acid  water.     No 
deflection.     This  indicates  that  particles  charged, 
or  otherwise,  suspended  in  a  conducting  solu- 
tion   (i.e.,    enclosed    within    our    hypothetical 
conducting  sphere)  are  not  affected  by  electro- 
static forces  without. 

5.  Cell  contained  ore  and  nitric  acid  solution 
to  generate  gas.     Neither  bubble  rising  nor  ore 
particles  dropping  showed  deflection.     Potential, 
10,000    volts.     The    conditions    here    duplicate 
those  of  No.  4. 

6.  Bubbles  blown  through  canvas  into  water 
or  acid  solution  were  not  deflected.     A  charge 
of  bubbles  flowing  in  one  direction  would  pro- 
duce an  electric  current,  and  even  if  they  were 
charged  they  could  not  be  attracted,   as  here 
again  the  charges  are  enclosed  in  a  conducting 
material. 

7.  Ore  poured  into  cell  containing  gasoline. 
There  seemed  to  be  a  slight  deflection.     10,000 
volts  between  plates.     Conditions  here  should 
not  differ  greatly  from  those  of  No.  3.     Solution 
may  not  have  been  sufficiently  non-conducting. 

8.  Solution    placed    in    electrolytic    cell,    ar- 


64  THE   THEORY  OF  FLOTATION 

ranged  as  shown,  gave  no  deflection  of  ore  or 
bubble  with  conducting  or  non-conducting  solu- 
tion. Both  ions  and  charged  colloids  are  sus- 
ceptible to  this  treatment,  and  no  doubt  they 
would  move  easier  than  the  large  body  and  so 
lessen  the  potential  on  the  larger  masses. 

9.  The  water  itself  was  electrolyzed  to  furnish 
gas.     A  two-way  switch  gave  either  hydrogen 
or  oxygen  at  the  bottom  pole,  which  was  covered 
with  a  layer  of  ore.     Both   gases   carried   ap- 
parently   equal    amounts    of    ore    with    equal 
readiness.     Bubbles  in  either  case,  upon  striking 
the  upper  plate,  did  not  discharge  their  burden 
of  ore,  no  matter  what  the  sign  of  electrode. 

10.  Set  up  as  in  No.  9,  except  that  gas  was 
furnished  by  action  of  nitric  acid  on  ore.     Chang- 
ing of  sign  produced  no  discernible  effect  upon 
bubble  or  ore  or  upon  bubbles  with  load  when 
coming  in  contact  with  upper  electrode  plate. 


Preferential  Flotation 

The  term  "  Preferential  Flotation  "  has.  often 
been  confused  with  that  of  "  Selective  Flo- 
tation. "  "  Preferential  flotation  "  is  the  term 
applied  to  that  process  by  which  one  mineral  is 
separated  from  another,  both  being  amenable 
to  the  flotation  treatment.  "  Selective  flota- 
tion," on  the  other  hand,  means  the  flotation 
of  a  valuable  mineral  in  the  presence  of  waste 
material.  Making  a  froth  concentrate  of  galena 
and  blende  from  a  lead-zinc  ore  is  a  sample  of 
selective  flotation,  but  if  two  separate  con- 
centrates, one  containing  a  high  percentage  of 
lead  and  the  other  a  high  percentage  of  zinc, 
are  made  by  means  of  two  or  more  different 


ROASTING   PROCESS  65 

treatments,  the  process  would  be  "  preferen- 
tial/' * 

So  far  the  chief  methods  of  preferential  flota- 
tion can  be  classified  into  these  three  groups: 
1.  Roasting  Methods.  2.  The  Use  of  a  Chemical 
Solution.  3.  Controlling  Flotation. 

Roasting  Process.  —  The  roasting  process  was 
developed  chiefly  by  Wentworth,  Ramage,  and 
Horwood.  This  process  really  consists  in  the 
deadening  of  certain  sulphides  by  short  and 
slight  roasts,  while  other  sulphides,  which  may 
be  present,  remain  unaffected  by  the  heat. 
Ramage  terms  this  "  fractional  roasting/'  while 
Horwood  speaks  of  it  as  "  preferential  flotation." 
The  Horwood  process  of  preferential  flotation  is 
practically  the  same  as  the  processes  of  Went- 
worth and  Ramage. 

The  Wentworth  Process: 

"  The  process  consists  in  the  preliminary 
treatment  of  ore  mixtures  containing  several 
sulphides,  which  converts  some  of  the  sulphides, 
superficially  at  least,  into  metallic  compounds 
which  are  differentiated  in  their  behavior  "  with 
respect  to  flotation  processes  as  commonly  prac- 
ticed. To  the  words  of  a  later  patentee,  the 
surfaces  of  such  minerals  as  galena,  pyrite,  and 
chalcopyrite  are  "  deadened  "  by  a  very  short 
and  slight  roast  in  a  roasting  furnace,  while  the 
sphalerite  is  unaffected.  Thus  the  sphalerite 
can  be  removed  by  flotation  from  such  an  ore, 
leaving  the  other  sulphide  minerals  to  be  removed 
by  other  means.  A  few  minutes  heating  at  a 
dull-red  heat  has  been  found  to  be  sufficient. 

1  "Advancement  and  Present  Status  of  Preferential 
Flotation, "  by  H.  J.  Stander,  Min.  &  Eng.  World,  Nov.  18, 
1916. 


66  THE  THEORY  OF  FLOTATION 

The  Ramage  Process: 

"  This  process  has  for  its  object  the  separation 
of  the  valuable  minerals  from  such  ore  as  chal- 
copyrite, bornite,  or  erubescite,  and  mixtures  of 
the  same  with  pyrite,  in  which  ores  the  copper 
is  in  chemical  combination  with  the  iron;  and 
also  from  such  ores  containing  zinc  blende.  The 
method  is  also  applicable  to  compound  ores, 
such  as  those  of  the  Cobalt  district  and  other 
sulph-arsenides."  "  The  principle  of  the  process 
is  founded  on  the  combination  of  fractional 
roasting  with  chemical  floating/7  Ramage's 
introduction  of  the  term  "  fractional  roasting  " 
is  particularly  felicitous,  as  it  more  accurately 
describes  the  method  than  does  the  term  "  pref- 
erential flotation/ '  used  by  Horwood. 

Ramage  described  the  process  by  the  use  of 
three  examples,  which  are  decidedly  interesting. 
The  first  example  is  of  an  ore  containing  iron 
pyrite  and  chalcopyrite,  with  a  content  of  about 
5  per  cent  copper  and  30  to  40  per  cent  sulphur. 
The  ore  is  roasted  at  about  a  red  heat  long 
enough  to  decompose  the  pyrite  slightly  and 
not  affect  the  chalcopyrite.  "  The  burnt  ore  is 
then  crushed  to  at  least  15  mesh  and  passed 
through  a  solution  of  acid  sulphate  of  soda  and 
nitric  acid  (the  solution  being  formed  by  adding 
nitric  acid  to  sulphate  of  soda),  which  solution 
is  kept  near  the  boiling  point.  The  copper 
sulphide  immediately  rises  to  the  top  of  the 
bath  and  can  be  slammed  off."  The  copper 
dissolved  in  the  bath  can  be  recovered  in  known 
ways.  This  method  of  flotation  (hot  acid  bath) 
is  not  new,  having  been  patented  by  DeBavay, 
Potter,  Delprat,  and  others.  The  fractional 
roasting  had  been  previously  patented  by  Went- 
worth,  and  so  the  only  thing  that  seems  new  is 
the  combination  of  methods. 

A  second  example  is  that  of  an  ore  containing 


ROASTING  PROCESS  67 

pyrite,  chalcopyrite,  and  zinc  blende  in  quantity. 
The  ore  is  roasted  at  a  temperature  of  not 
over  600°  C.,  so  that  only  the  iron  pyrite  is 
deadened.  The  roasted  ore  is  then  subjected  to 
the  acid  sulphate  of  soda  solution  for  flotation 
of  the  unchanged  sulphides  of  zinc  and  of  copper. 
This  product  is  then  roasted  at  about  700°  C., 
until  all  of  the  zinc  sulphide  is  decomposed  and 
the  copper  sulphide  unchanged.  This  mixture 
is  treated  with  a  solution  of  dilute  sulphuric  acid 
for  the  dissolution  of  the  zinc,  to  be  recovered 
from  solution  by  any  familiar  process,  such  as 
electrolysis,  the  copper  sulphides  being  sent  to 
the  copper  smelter.  There  are  certainly  most 
interesting  facts  disclosed  in  this  patent.  The 
great  resistance  of  copper  sulphides  to  the  roast- 
ing process,  as  compared  with  the  sulphides  of 
zinc,  is  something  new  and  will  be  a  most  valu- 
able characteristic,  if  true. 

The  third  example  is  that  of  the  ores  of  the 
Cobalt  district,  Canada,  where  cobaltite,  nic- 
colite,  chalcopyrite,  pyrite,  and  native  silver 
occur.  All  the  sulphide  and  sulpharsenide 
minerals  are  floated,  leaving  the  silver  in  the 
gangue.  The  sulphides  are  roasted  at  about 
800°  C.  and  everything  is  decomposed  except 
the  copper  sulphide,  which  can  be  floated  from 
the  calcine.  Again  we  have  mention  of  the 
almost  incredible  property  of  copper  sulphides 
to  resist  roasting. 

The  next  patent  was  that  of  H.  A.  Wentworth, 
amplifying  on  this  former  patent  in  claiming  the 
chemical  change  of  minerals  as  a  method  of 
separating  them  preferentially  by  flotation.  He 
had  in  mind  particularly  the  treatment  of  the 
ore  with  chlorine,  which  would  sink  when  sub- 
jected to  a  film-flotation  process,  while  others 
would  have  their  flotative  properties  enhanced. 
As  an  example,  a  mixture  of  zinc  and  iron  sul- 
phides, when  treated  with  chlorine  gas  in  a 


68  THE   THEORY  OF  FLOTATION 

slightly  damp  state,  is  so  altered  that  the 
blende  will  float  on  a  film-flotation  machine 
much  better  than  before  treatment,  while  the 
pyrite  has  a  coating  formed  over  its  surface 
which  is  much  more  easily  wetted,  so  that  it 
will  sink.  Still  a  further  example  is  the  appli- 
cation to  the  separation  of  pyrite  and  chal- 
copyrite.  The  latter  is  attacked  much  slower 
than  pyrite;  hence  it  can  be  floated  when  both 
are  present.  A  similar  behavior  of  the  minerals 
is  observed  when  they  are  suspended  in  water 
containing  dissolved  chlorine  in  the  proper  con- 
centration, but  the  best  work  seems  to  be  done 
with  minerals  fed  onto  one  of  the  film-flotation 
machines,  such  as  that  of  H.  E.  Wood  of  Denver, 
although  Wentworth  gives  the  design  of  one  of 
his  own  in  the  specification.  It  is  easy  to  see 
that  with  chlorine  water  and  one  of  the  me- 
chanical frothing  methods  of  flotation  the  soluble 
coatings  that  are  formed  on  the  surfaces  of  the 
minerals  would  be  simply  washed  off  and  the 
preferential  part  of  the  flotation  lost.  Tests  in 
our  laboratory  seem  to  show  this.  So  far  as  is 
known  to  me,  this  process  is  not  being  used. 

The  Horwood  Process: 

It  depends  upon  the  "  deadening  "  of  galena 
and  pyrite  in  a  short  roasting  at  300  to  500°  C., 
whereby  the  galena  is  coated  with  lead  sulphate 
and  the  pyrite  with  iron  oxide,  while  the  sphal- 
erite is  unaltered.  This  allows  a  separation  of 
the  undesirable  zinc  from  the  lead-iron-silver 
product  and  allows  their  separate  marketing. 
This  process  has  received  more  careful  attention 
than  any  other  process,  and  reference  to  original 
articles  is  best.1  According  to  the  data  given  in 

1  T.  J.  Hoover,  "Concentrating  Ores  by  Flotation," 
Min.  &  Eng.  World,  July  18,  1914;  Eng.  &  Min.  Jour. 
(1914),  97,  p.  1208;  Min.  &  Sci.  Press,  April  18,  1914, 
p.  657;  Metal.  &  Chem.  Eng.  (1914),  No.  12,  pp.  350  and 
592. 


ROASTING   PROCESS  69 

some  of  this  literature,  it  appears  that  it  is 
possible  to  take  a  flotation  concentrate  contain- 
ing 36  per  cent  Zn,  15  per  cent  Pb,  and  22  oz. 
Ag  per  ton,  and  divide  it  into  a  zinc  product 
running  as  high  as  50  per  cent  Zn,  7  per  cent  Pb, 
and  15  oz.  Ag,  and  a  lead  product  containing 
38  per  cent  Pb,  8  per  cent  Zn,  and  42  oz.  Ag 
per  ton.  This  is  of  great  interest  to  all  pro- 
ducers of  " complex  sulphide"  ores,  as  the  mill- 
ing of  coarsely  crystalline  material  has  presented 
much  difficulty  in  the  past  for  the  reason  that 
some  finely-divided  material  (slime)  is  bound  to 
form  in  crushing,  and  while  the  combined  lead 
and  zinc  sulphides  can  be  floated  nowadays 
without  much  difficulty,  the  mixture  is  of  far 
less  value  than  the  two  minerals  separated. 
This  is  important  enough,  not  to  speak  of  the 
possibility  of  treating  the  microcrystalline  sul- 
phide ores  and  those  containing  gangue  of  high 
specific  gravity,  such  as  barite.  While  flo- 
tation has  been  a  boon  to  the  concentration  of 
all  sulphide  slimes,  preferential  flotation  is  much 
more  important  for  the  ores  containing  unde- 
sirable combinations  of  sulphides.  Hence  Hor- 
wood's  work  should  receive  the  highest  praise. 

Another  detail,  as  regards  the  process,  is  that 
35  Ib.  of  sulphuric  acid  per  ton  of  ore  is  neces- 
sary and  2  to  3  Ib.  of  oleic  acid  for  the  flotation 
of  the  unaltered  zinc.  All  of  this  appeared  in 
Horwood's  first  patent,  No.  1,020,353,  of  1912, 
and  he  later  came  out  with  improvements  on 
the  process  in  patent  No.  1,108,440,  of  1914. 
In  this  later  patent  he  stated  that  he  had  found 
there  was  a  tendency  for  the  silver  to  follow 
the  zinc,  which  is  undesirable,  but  that  this 
could  be  prevented  by  simply  washing  away  all 
soluble  salts  on  the  concentrate  before  it  was 
subjected  to  the  deadening  roast.  This  re- 
duces the  amount  of  oxidized  zinc  formed  and 
lost  by  solution  in  the  dilute  acid  in  the  mill- 


70  THE   THEORY  OF  FLOTATION 

water  as  well  as  allowing  the  silver  to  become 
deadened  to  a  greater  extent.  He  also  found 
that  the  most  successful  flotation  took  place 
with  the  pulp  at  a  temperature  of  about  120°  F. 

It  will  be  seen  that  the  Horwood  process  has 
been  applied  only  to  concentrates  from  previous 
flotation  or  from  other  concentration  processes. 
This  is  the  logical  place  to  apply  it,  as  there  is 
no  object  in  leaving  a  non-flotative  galena  or 
other  sulphide  mixed  with  gangue,  by  using  the 
process  on  crude  ore.  The  same  remark  applies 
to  many  of  the  other  processes.  To  be  sure, 
there  has  been  some  success  in  the  Australian 
mills  as  well  as  in  the  United  States  in  the  treat- 
ment of  mixed  galena-sphalerite  concentrates 
from  flotation  machines  on  concentrating  tables. 
As  an  example,  the  Timber  Butte  mill  is  treating 
the  flotation  concentrate  of  a  zinc  ore  containing 
some  zinc  concentrate  carrying  53  per  cent  Zn, 
1.5  per  cent  Pb,  and  4  per  cent  insoluble.  How- 
ever, this  method  has  not  always  met  with  the 
best  results,  and  where  the  proportions  of  lead 
and  zinc  in  ordinary  complex  sulphide  concen- 
trates are  about  equal  it  is  quite  hard  to  get  two 
products  that  are  sufficiently  pure.  Where  it 
can  be  done,  it  is  certainly  more  desirable  than 
the  more  complex  fractional  roasting  and  prefer- 
ential flotation  processes  of  Horwood,  Went- 
worth,  and  Ramage. 

The  Use  of  Chemical  Solution. —  In  the 
Lyster  process  the  preferential  action  is  brought 
about  by  the  use  of  a  chemical  solution.  This 
process  has  received  some  consideration  by 


ROASTING  PROCESS  71 

the  Zinc  Corporation.  The  process  is  as 
follows : 

This  process  is  carried  on  in  neutral  or  alkaline 
solutions  (never  acid)  of  the  sulphates,  chlorides, 
or  nitrates  of  calcium,  magnesium,  zinc,  iron, 
acid  sodium,  or  sodium-potassium  sulphates. 
Using  eucalyptus  oil  or  a  similar  frothing  agent, 
the  agitation  of  the  pulp  takes  place  in  centrif- 
ugal pumps,  throttled  to  give  further  agitation, 
and  discharging  into  spitzkasten  with  constricted 
tops.  It  is  said  that  a  galena  froth  can  be 
collected  carrying  55  to  60  per  cent  lead  and 
that  by  sending  the  tailing  to  a  second  machine 
with  further  addition  of  oil,  the  sphalerite  can 
be  floated. 

It  will  be  noticed  that  this,  with  the  possible 
exception  of  Wentworth's  second  patent,  is  one 
of  the  first  proposals  to  give  a  true  "  preferen- 
tial "  flotation  to  a  mixture  of  sulphides,  as  the 
roasting  methods  above  mentioned  involve  an 
actual  conversion  of  some  of  the  minerals,  so 
that  sulphide  surfaces  are  no  longer  presented 
to  the  oils  and  air  bubbles  in  the  flotation  opera- 
tion. Lyster's  process,  however,  involves  the 
actual  flotation  of  one  mineral  in  preference  to 
another,  unless  the  chemicals  used  are  chemically 
altering  certain  of  the  sulphides  so  that  they 
cannot  float.  Anyone  who  has  worked  with 
mixtures  of  sulphides  has  doubtless  noticed  that 
greater  care  is  necessary  in  the  flotation  of  zinc 
sulphide  than  in  floating  galena;  in  fact,  galena 
is  one  of  the  most  easily  floated  minerals  outside 
of  molybdenite,  and  zinc  sulphide  is  considerably 


72         'THE  THEORY  OF  FLOTATION 

more  difficult.  The  fact  that  a  froth  running  so 
high  in  lead,  as  the  Lyster  process  is  reported 
to  give,  would  also  tend  to  make  one  suspi- 
cious that  rather  poor  flotation  conditions  are 
maintained,  so  that  only  the  most  easily  floated 
material  (galena),  and  only  the  purest  of  that,  is 
coming  up  in  the  first  product.  This  takes 
place  even  in  the  presence  of  considerable  oil, 
whenever  flotation  conditions  are  poor,  on  almost 
any  type  of  machine,  and  while  the  grade  of 
froth  that  is  obtained  is  high,  the  extraction  is 
poor  on  account  of  the  fact  that  only  the  best 
mineral  is  floating.  It  is  possible  that  some 
such  combination  of  results  as  this  has  caused 
the  process  not  to  be  considered  unfavorably. 

Controlling  Flotation.  —  It  is  a  known  fact 
that  the  percentage  of  extraction  by  flotation 
of  a  sulphide  in  an  ore  depends  on  such  factors 
as  the  degree  of  fineness  of  the  gangue  and  of  the 
mineral  particles  and  so  also  do  some  of  the  other 
variables  such  as  the  amount  and  kind  of  oil 
or  acid  used,  the  time  and  speed  of  agitation  and 
the  temperature  at  which  the  experiment  is  con- 
ducted. And  furthermore,  we  know  that  one  sul- 
phide is  more  flotative  than  another,  a  very  impor- 
tant property  in  this  particular  phase  of  flotation. 

In  1913  Nutter  and  Lavers  made  use  of  these 
different  behaviors  of  sulphides  under  different 
conditions,  and  brought  out  their  process  for 
preferential  flotation  of  minerals.  It  is  "a 
process  for  concentrating  ores  which  consists 
in  treating  the  crushed  ore  by  a  flotation  process, 
two  or  more  times  under  different  conditions, 


CONTROLLING  FLOTATION  73 

to  obtain  froths  or  scums,  having  the  constitu- 
ents of  each  in  certain  ratios  of  size,  and  there- 
after subjecting  the  powdered  mixture  contained 
in  each  froth  to  a  classifying  step  to  separate  the 
constituents."  According  to  the  description 
of  their  process,  the  one  sulphide  can  be  sepa- 
rated from  the  other  by  correctly  controlling 
certain  conditions  in  the  flotation  plant. 

The  following  is  an  example  cited  by  the  in- 
ventors: 

An  ore,  containing  galena,  chalcopyrite,  and 
sphalerite,  is  crushed  and  admitted  to  the  ^flo- 
tation machine.  Using  cresylie  acid  without 
any  mineral  acid,  it  is  possible  to  float  most  of 
the  chalcopyrite  and  a  small  quantity  of  galena. 
So,  from  this  first  treatment,  a  chalcopyrite 
concentrate  is  obtained,  the  residue  being  given 
a  second  treatment,  and  with  the  help  of  sul- 
phuric acid,  a  galena  froth  concentrate  can  be 
produced,  most  of  the  sphalerite  being  left  in  the 
tailings,  from  which  it  can  then  be  recovered. 
In  case  the  ore  contains  only  copper  and  zinc 
sulphides,  a  preferential  action  can  be  produced 
by  the  use  of  eucalyptus  oil  or  creosol.  No 
mineral  acid  is  necessary,  and  a  concentrate, 
containing  most  of  the  chalcopyrite  and  very 
little  sphalerite,  can  be  obtained. 

In  a  method  where  the  separation  of  one 
mineral  from  another  depends  largely  on  certain 
conditions,  the  process  becomes  somewhat  deli- 
cate, especially  in  the  case  of  flotation.  Never- 
theless it  seems  as  if  this  is  one  of  the  chief  ways 
in  which  preferential  flotation  will  be  successfully 
developed  in  the  future. 

/The  phenomena  in  connection  with  preferen- 


74  THE  THEORY  OF  FLOTATION 

tial  flotation,  according  to  Thomas  M.  Baines, 
Jr.,  furnish  new  evidence  to  strengthen  the 
electrical  theory.  The  following  interesting 
material  is  taken  from  his  article:1 

The  simplest  experiment,  demonstrating  pref- 
erential flotation,  may  be  performed  as  follows: 
Upon  a  4-in.  watch-glass,  place  a  little  galena, 
blende,  and  quartz  of  20  to  30-mesh  size.  Add 
dilute  nitric  acid  and  place  the  glass  under  a 
microscope.  The  acid  attacks  the  galena,  form- 
ing bubbles  of  H2S  gas  that  adhere  to  the  galena. 
The  particles  of  galena  are  electrified  also,  as  can 
be  seen  by  the  actions  of  the  particles.  The 
blende  and  quartz  are  not  attacked.  If  the  ore 
had  been  finely  pulverized  and  dilute  nitric  acid 
added,  the  bubbles  of  H2S  would  have  been 
sufficient  to  float  the  galena,  leaving  the  blende 
and  quartz  at  the  bottom.  However,  with  fine 
particles,  some  blende  and  quartz  would  have 
been  entrapped,  brought  to  the  surface,  and 
held  there  by  surface  tension.  The  bubbles  are 
not  sufficient  to  float  the  coarse  galena,  but  by  a 
vanning  motion  of  the  glass,  the  galena  will 
collect,  being  brought  and  held  together  by  the 
H2S  bubbles,  forming  a  mat  which  is  lighter  / 
than  quartz  or  blende  and  can,  therefore,  be 
panned  off,  leaving  the  blende  and  quartz. 
This  experiment  seems  to  show  that  the  H2S  is 
charged  oppositely  to  the  galena. 

If  more  concentrated  nitric  acid  had  been 
added  to  the  ore,  the  blende  would  have  been 
attacked  and  the  process  would  have  been  re- 
versed, the  blende  forming  the  mat  while  galena 
and  quartz  were  left  behind.  If  dilute  sulphuric 
acid,  one  part  of  acid  to  four  of  water,  had  been 
used,  then  both  the  blende  and  galena  would 

1  "  The  Electrical  Theory  of  Flotation,"  Min.  &  Sci. 
Press,  December  11,  1915.  s 


CONTROLLING  FLOTATION  75 

have  been  attacked  and  if  the  ore  had  been 
finely  pulverized,  no  "  preferential  "  separation 
would  have  resulted,  both  galena  and  blende 
finding  their  way  into  the  float  concentrate. 
However,  with  coarse  material,  the  blende  is 
much  more  highly  charged  than  the  galena  and 
if  the  watch-glass  be  tapped  and  the  contents 
given  a  vanning  motion,  the  blende  will  gather 
most  of  the  H2S  bubbles  and  finally  float,  leaving 
galena  and  quartz  behind.  This  shows  that 
the  electrification  of  minerals  varies  with  differ- 
ent acids  and  also  with  different  strengths  of  the 
same.  This  action  of  one  mineral,  "  robbing  " 
the  others  of  their  bubbles,  has  not  been  utilized 
in  practice,  as  yet,  but  there  is  no  reason  why 
"  preferential "  separations  could  not  be  made 
on  a  large  scale,  utilizing  this  principle.  Less 
air  or  gas  would  be  necessary  than  in  the  present 
type  of  frothing  cells  and  a  clean  concentrate 
would  be  produced  at  once.  A  separation  of 
blende,  galena,  pyrite,  and  quartz  may  be  made 
as  follows: 

Add  dilute  sulphuric  acid  and  pan  off  the 
blende;  then  add  dilute  nitric  acid  and  pan  off 
the  galena;  then  add  concentrated  sulphuric 
or  nitric  acid,  which  attacks  the  pyrite  so  that  it 
may  be  panned  off. 

Or  the  separation  may  be  made  with  nitric  acid 
alone,  varying  the  strengths;  with  sulphuric 
acid,  by  use  of  the  "  robbing  "  action  described 
above  or  by  use  of  hydrochloric  and  other  re- 
agents that  attack  one  or  another  of  the  minerals 
more  strongly  than  the  others.  If  galena  or 
blende  and  magnetite  be  treated  with  dilute  sul- 
phuric acid,  the  magnetite  will  not  be  acted  upon 
by  the  acid,  but  some  of  the  H2S  bubbles  gener- 
ated by  the  sulphide  will  attach  themselves  to 
the  magnetite,  provided  the  bubble  is  formed 
near  the  magnetite.  This  illustrates  the  fact 
that  electrical  conductors  in  a  conducting  liquid 


76  THE  THEORY  OF  FLOTATION 

attract  electrified  bubbles.  A  slight  jar,  how- 
ever, will  displace  these  bubbles;  or  a  piece  of 
sulphide  in  close  proximity  will  rob  the  magne- 
tite of  the  bubble,  magnetite  being  a  poor  con- 
ductor. 

Referring  to  the  article  on  page  668  of  the 
Mining  and  Scientific  Press  of  October  30,  1915, 
describing  a  patent  for  preferential  flotation  of 
blende,  galena,  and  pyrite,  the  second  paragraph 
read:  "  The  new  process  consists  of  treating 
ores  in  a  medium  (i.e.,  sulphuric  acid  and  sodium 
sulphide)  that  wets  the  zinc  sulphide  and  which 
does  not  wet  the  lead  sulphide  or  pyrite. "  This 
phenomenon  brings  out  nicely  the  part  played 
in  flotation  by  the  "  dielectric  film."  When 
thiosulphates,  sulphites,  or  bisulphites  are  acted 
upon  by  sulphuric  acid,  there  is  more  to  the 
phenomenon  than  formation  of  SO2  gas.  The 
following  reactions  take  place  when  blende  and 
galena  are  treated  with  sulphuric  acid  and  so- 
dium sulphide : 

ZnS+PbS+2  H2S04  =  ZnS04  +  PbS04+2  H2S, 
Na2S02+  H2S04  =  Ns2S04+H20+S02, 
2  H2S+S02  =  2  H20+3S. 

This  sulphur  thus  formed  is  in  a  very  fine 
state  and  acts  as  a  dielectric  film  about  the 
galena,  for  which  it  had  a  great  attraction. 
Therefore,  no  frothing  agent  is  needed  in  this 
case,  as  the  dielectric  film  about  the  bubbles  is 
formed  by  the  sulphur  similarly  to  the  films 
of  oil  formed  in  the  ordinary  flotation  processes. 
In  the  last  paragraph  of  the  above-mentioned 
article  on  "  Preferential  Flotation,"  the  statement . 
is  made  that  "  the  procuring  of  the  effect  aimed 
at,  is  dependent  upon  the  presence  of  a  frothing 
agent,  only  when  a  reducing  gas  is  introduced 
into  the  medium.  It  is  not  independent  of  the 
presence  of  a  frothing  agent  in  the  flotation 


CONTROLLING  FLOTATION  77 

medium,  when  a  reducing  gas  is  generated  in  the 
flotation  medium  by  a  reaction  of  a  substance 
introduced  into  it."  In  other  words,  if  sulphur 
or  any  other  "  dielectric  "  is  liberated  in  a  very 
fine  state,  by  a  "  reaction  of  a  substance  in- 
troduced/7 no  frothing  agent  need  be  used. 

This  action  may  be  nicely  illustrated  by 
taking  20-  to  30-mesh  galena  and  blende  and 
treating  them  with  dilute  nitric  acid  on  a  watch- 
glass  and  observing  the  result  under  a  micro- 
scope. The  galena  will  gather  all  the  H2S  bub- 
bles, when  vanned.  Now  if  the  sulphuric  acid 
is  added  and  the  watch-glass  be  tapped  and  the 
particles  moved  over  one  another,  the  H2S 
bubbles  on  the  galena  will  be  robbed  by  the 
blende.  Sulphur  may  be  seen  surrounding  the 
bubbles,  the  reaction  being  as  follows: 

ZnS  +PbS  +  2  H2S04  =  ZnS04  +  PbS04  +  2  H2S, 

HoS  +  H2S04  =  S02  +  2  H20  +  S,       (1) 

2  H2S  +  S02  =  2  H2O  +  3  S.  (2) 

In  (1)  the  sulphur  is  formed  from  the  decom- 
position of  H2S;  and  would  be  charged  oppositely 
to  the  sulphur  formed  by  the  decomposition  of 
S02  gas.  In  (2)  we  have  both  negatively  and 
positively  charged  sulphur  particles. 

In  conclusion,  Mr.  Baines  states: 

It  may  be  well  to  call  attention  to  the  fact  that 
for  laboratory  experiments  in  preferential  flo- 
tation, any  one  of  the  sulphides  may  be  separated 
from  the  other  sulphides,  (a)  by  the  use  of  gome 
reagent  that  attacks  this  particular  sulphide 
and  not  the  others,  (6)  by  the  use  of  a  reagent 
that  attacks  one  sulphide  more  vigorously  than 
the  others  (in  this  case,  the  vanning  motion 
allows  the  sulphide  more  highly  charged  to 
gather  up  the  bubbles  from  the  sulphides  less 
highly  charged,  and  if  sufficient  bubbles  are  col- 
lected, the  mass  of  bubbles  and  sulphides  will 


78  THE  THEORY  OF  FLOTATION 

float).  If  not  sufficiently  buoyed,  the  mass 
remains  submerged,  but  it  is  lighter  than  the 
other  sulphides  of  gangue  minerals  and  can  be 
panned  off  or  separated  by  hydraulic  classi- 
fication. 

The  second  point  of  interest  is  the  formation 
of  a  frothing  agent  within  the  pulp,  when  reac- 
tions take  place  that  liberate  dielectric  sub- 
stances in  a  very  fine  state,  electrically  charged. 

The  third  point  is  that  laboratory  experiments 
may  not  work  out  in  practice,  due  to  failure  to 
understand  the  nature  of  the  electrical  charges 
of  the  bubbles,  dielectrics,  and  particles  of  ore. 
A  little  stronger  reagent  or  a  different  way  of 
frictionally  electrifying  the  bubbles  and  pulp,  or 
too  thick  a  film  of  dielectric  or  frothing  agent, 
causes  the  attraction  to  cease  or  change.  It  is 
no  wonder  that  great  difficulty  has  been  ex- 
perienced'in  the  practical  application  of  flotation 
to  ores,  when  such  delicate  electric  forces  have 
to  be  considered. 


CHAPTER  IV 
THE  FLOTATION  OF  OXIDIZED  ORES 

Concentration  of  natural  sulphide  ores  by  the 
flotation  process  has  met  with  such  success  that 
attempts  have  recently  been  made  to  apply  the 
process  to  the  flotation  of  ores  other  than  natural 
sulphides. 

A  recent  article  by  0.  C.  Ralston  and  Glen  L. 
Allen1  covers  quite  thoroughly  the  work  done 
on  the  subject  up  to  date,  and  what  follows  is 
largely  taken  from  their  work. 

Flotation  of  oxidized  minerals  depends  upon 
preliminary  "  sulphidizing "  by  any  method 
that  will  convert  at  least  the  surface  of  the 
mineral  particles  to  a  sulphide  of  the  metal. 
This  step  is  followed  by  flotation  of  the  artificial 
sulphide,  which  results  in  a  concentration  of  the 
valuable  metals  in  the  low-grade  oxidized  ore 
being  treated. 

The  methods  of  sulphidizing  so  far  investigated 
are  as  follows: 

1.  By  the  use  of  hydrogen  sulphide  on  either 
the  dry  or  wet  crushed  ore. 

2.  By  the   use   of   solutions  of  the  various 
sulphides    and    sulpho-compounds    of    sodium. 

3.  By  the   use   of  solutions  of  the  various 
sulphides  and  sulpho-compounds  of  calcium. 

1  "The  Flotation  of  Oxidized  Ores,"  by  O.  C.  Ralston 
&  Glen  L.  Allen,  Min.  &  Sci.  Press,  July  29,  1916. 
79 


80  FLOTATION  OF  OXIDIZED   ORES 

4.  By  the  use  of  a  sulphur  vapor. 

5.  By  the  use  of  a  sulphuretted  oil. 

6.  With  colloidal  sulphur. 

It  has  been  found  that  treatment  by  some  of 
these  methods  will  form  a  film  of  sulphide  over 
the  surface  of  the  particles  of  such  minerals  as 
lead  carbonate  or  copper  carbonate,  whereas 
in  the  other  cases  the  mineral  particles  are 
sulphidized  to  the  core.  Other  methods  failed. 

By  the  Use  of  Hydrogen  Sulphide.  —  In  sul- 
phidizing  with  hydrogen  sulphide  gas,  as  applied 
to  lead-carbonate  ores/  the  best  method  of  ap- 
plying the  hydrogen  sulphide  gas  is  in  a  tumbling 
barrel  with  the  gas  inlet  in  the  end.  It  is  also 
found  that  a  low  extraction  and  likewise  a  low- 
grade  concentrate  of  lead  is  obtained  if  an 
attempt  is  made  to  float  the  blackened  sulphide 
(after  treating  with  H2S)  without  previously 
acidifying  the  pulp.  The  concentrate  is  cleaner 
but  the  extraction  still  low.  Only  by  prolonged 
treatment  by  H2S  gas  can  the  extraction  of  lead 
be  raised  to  commercial  grade. 

Hydrogen  sulphide  can  be  generated  quite 
cheaply.  With  iron  matte  available  at  $5  to 
$10  per  ton,  the  cost  of  the  H2S  gas  resulting, 
including  labor,  etc.,  is  between  $30  and  $50 
per  ton.  A  ton  of  H2S  gas,  if  it  were  not  for  the 
fact  that  the  gas  attacks  the  metallic  particles 
of  the  ore  with  such  avidity  that  by  the  time 
the  latter  are  sulphidized  sufficiently  to  permit 
of  good  extraction  by  flotation,  they  have  been 
sulphidized  to  the  core,  could  be  made  to  film 
many  tons  of  ore. 


SODIUM   AND   CALCIUM  81 

Owing  to  the  fact  that  the  value  of  lead  con- 
centrate obtained  is  very  low  as  compared  to  the 
amount  of  H2S  necessary  to  sulphidize  it,  this 
process  is  not  regarded  as  commercially  practi- 
cable. 

Joseph  T.  Terry,  Jr.,  states: 

That  H2S  gas  is  the  most  satisfactory  reagent 
and  can  be  cheaply  produced  without  the  use 
of  acids  by  the  destructive  distillation  of  nu- 
merous organic  substances  mixed  with  sulphur, 
and  that  the  sulphide  filming  of  the  carbonate 
minerals  is  best  accomplished  by  introducing  the 
gas  into  the  ore  pulp  crushed  to  80  mesh,  with 
a  density  *of  20  per  cent  solid,  kept  in  motion 
or  agitation  in  an  enclosed  agitator,  or  other 
suitable  apparatus,  this  paralleling  conditions 
when  using  a  solid  sulphide. 

By  the  Use  of  Solutions  of  Sulphides  and  Sul- 
pho-compounds  of  Sodium  and  Calcium.  — 

Good  results  on  lead-carbonate  ores  have  been 
obtained  when  sulphides  of  sodium  calcium  were 
used  for  sulphidizing  agents;  also  sodium 
polysulphides  Na2S4,  and  Na2S5  and  the  sulph- 
hydrates  of  sodium,  calcium,  and  ammonium. 
Of  these  the  sulph-hydrates  seem  to  be  very 
effective.  Different  ores  require  10  minutes  to 
24  hours  of  contact  with  the  solutions  of  sodium 
sulphide,  depending  upon  the  properties  of  the 
ore  and  the  strength  of  the  solution,  10  to  20  Ib. 
per  ton  of  ore  usually  being  sufficient,  and  should 
be  applied  to  pulp  containing  about  one  ton  of 
water  per  ton  of  ore.  When  a  good  black  color 
has  developed,  and  the  color  has  ceased  to  increase 
in  thickness,  the  pulp  is  diluted  with  water 


82  FLOTATION   OF  OXIDIZED  ORES 

to  a  3  :  1  or  4  :  1  mixture  and  floated  in  either 
mechanically  agitated  or  pneumatic  machines. 

By  the  Use  of  Sulphur  Vapor.  —  Sulphidizing 
with  sulphur  vapor  has  been  tried  with  little 
success,  for  the  reason  that  it  must  be  applied 
at  a  temperature  above  the  boiling  point  of 
sulphur  in  order  to  prevent  condensation  of  sul- 
phur. This  means  that  the  ore  must  be  brought 
to  a  temperature  above  445°  C.  Pyrite  could 
be  used  to  furnish  the  necessary  sulphur,  for 
when  it  is  heated  in  a  closed  space,  it  gives  up 
half  of  its  sulphur.  Sulphur  dioxide  gas  can 
be  reduced  to  elemental  sulphur  by  passing  it 
through  a  heated  zone  in  the  presence  of  a  re- 
ducing agent. 

This  method  has  the  disadvantages  of  having 
to  be  applied  to  dried,  heated,  and  finely  divided 
ores.  Although  it  is  stated  that  sulphur  vapor 
was  tested  at  one  of  the  large  plants  for  flotation 
of  oxidized  forms  of  copper,  it  gave  better  results 
than  any  other  method  of  sulphidizing. 

On  oxidized  copper  ores  H2S  seems  to  be  by 
far  the  best  sulphidizing  agent.  It  is  best  ap- 
plied to  wet  pulp  and  seems  to  cause  true  filming. 
As  little  as  J  Ib.  of  sulphur  per  ton  of  ore  is 
giving  good  results  in  the  plant  of  the  Magma 
Copper  Company,  at  Magma,  Arizona. 

For  oxidized  copper  ores  containing  a  fraction 
of  1  per  cent  1)  2  to  3  Ib.  per  ton  of  ore  is  giving 
satisfactory  results. 

Calcium  polysulphide  has  been  used  for  some 
time  in  a  number  of  the  large  copper  concen- 

1  Sulphides  are  present,  of  course. 


THE  MAUREX  MAGNETIC  PROCESS       83 

trating  mills  with  indifferent  success,  and  seems 
to  be  detrimental  in  some  instances. 

By  the  Use  of  Sulphuretted  Oil. —  Much 
secrecy  is  observed  by  a  number  of  plants  using 
sulphuretted  oils  as  to  the  technical  details  of 
this  work. 

With  Colloidal  Sulphur.  —  Oxidized  forms  of 
copper,  so  far  as  is  known,  are  not  floated  by 
colloidal  sulphur.  Neither  have  the  silicates 
of  copper  been  floated. 

It  is  a  peculiar  fact,  but  repeated  attempts  to 
float  natural  sulphides  along  with  sulphidized 
minerals  ha^e  failed,  as  the  sulphidizing  agents 
cause  trouble  with  the  flotation  of  natural  sul- 
phides. By  careful  adjustment  this  difficulty  has 
been  solved  in  one  plant,  though  the  details  are 
not  available. 

The  treatment  of  zinc  ores  and  carbonates,  as 
a  whole,  has  been  unsuccessful.  The  sulphide 
film  does  not  adhere  very  strongly  and  hence 
comes  off  too  soon. 

So  far  as  the  writer  is  aware,  in  all  of  the  sue-- 
cessful  work  in  floating  oxides  and  carbonates, 
there  has  been  an  alteration  of  the  oxide  to  sul- 
phide. A  number  of  parties  claim  to  be  success- 
ful in  the  flotation  of  copper  carbonates  without 
sulphidizing,  and  others  in  the  flotation  of  schu- 
lite,  fluorite,  and  magnetite. 

The  Maurex  Magnetic  Process.  —  This  proc- 
ess was  invented  and  patented  by  A.  A.  Lock- 
wood.  Various  blendes  of  crude  oils  are  used  in 
the  proportion  of  15  to  20  Ib.  (or  f  to  1  per 
cent)  of  oil  per  ton  of  ore,  to  which  is  added 


84  FLOTATION  OF  OXIDIZED  ORES 

an  equal  quantity  of  magnetite,  ground  to  100 
mesh.  This  mixture  of  oil  and  magnetite  forms 
a  permanent  paint,  which,  no  matter  how  finely 
it  may  be  divided  or  broken  up,  will  always  be 
found  to  be  composed  of  the  two  substances  in 
the  same  ratio.  The  selective  affinity  of  the 
oil  in  the  magnetic  mixture  enables  it  to  adhere 
to  any  particle  of  valuable .  mineral,  either  sul- 
phide or  oxide,  contained  in  the  ore,  with  which 
it  may  come  in  contact,  forming  a  rich  mag- 
netic-oil-mineral mixture  containing  little  or 
no  worthless  gangue. 

In  practice  the  crushed  ore  and  water,  to- 
gether with  a  regulated  quantity  of  oil  mix- 
ture, are  fed  through  a  horizontal  tube  revolving 
slowly,  which  contains  several  hundred  pounds  of 
J-inch  rough  iron  shot.  The  shot  becomes 
oiled  and  collects  the  mineral  particles,  both 
fine  and  coarse,  in  the  form  of  a  paste  that  ad- 
heres. This  paste  is  continuously  broken  away 
from  the  shot  by  attrition  and  flows  with  the 
pulp  through  a  screen  at  the  opposite  end  of 
the  agitator  tube  into  a  shaking  tray  which  feeds 
it  under  a  powerful  electromagnet.  The  coated 
mineral  particles  are  attracted  by  the  magnet 
from  the  flowing  stream  of  pulp  to  the  under- 
side of  an  endless  belt  traveling  under  the  mag- 
net at  right  angles  to  the  shaking  tray,  thereby 
suspending  them  until  they  are  carried  out  of  the 
magnetic  field,  when  they  are  washed  off  by  a 
spray  of  water  into  the  concentrate  box  provided. 

The  points  of  advantages  claimed  for  this 
process  are  the  following: 


THE  MAUREX  MAGNETIC  PROCESS       85 

1.  The  ore  need  only  be  ground  fine  enough  to 
free  the  mineral  particles  from  the  gangue,  in 
some  cases  being  only  crushed  to  5  mm. 

2.  Both  sand  and  slime  are  treated  together 
in   one  operation,   so  that  no   classification  is 
necessary. 

3.  This  process  is  suited  to  the  treatment  of 
practically  all  the  sulphide  ore,  and  also  suc- 
cessfully   treats    lead,    copper,    and    zinc    car- 
bonates and  oxides,  making  extractions  up  to 
93  per  cent  in  some  cases. 


CHAPTER  V 

OIL  AND  OTHER  REAGENTS  IN  FLO- 
TATION 

Oils  Used  in  Flotation.  —  The  question  of 
what  oils  to  use  in  flotation  has  probably  given 
more  trouble  from  a  practical  standpoint  than 
any  other.  In  some  cases  the  situation  has  been 
something  like  this:  The  manufacturer  or 
producer  of  oils  cannot  get  any  definite  ideas  as 
to  what  kinds  or  qualities  of  oils  are  needed,  so 
he  sends  to  the  plant  superintendent  products 
or  mixtures  marked  "  240B  "  or  "  1000A,"  or 
whatever  he  happens  to  call  them,  with  little 
information  as  to  their  chemical  composition 
or  physical  qualities.  One  of  these  oils  is  used 
with  good  results,  although  he  has  no  information 
as  to  the  real  composition  or  the  physical  qualities 
that  have  given  him  the  results  obtained.  When 
he  needs  more  oil  he  naturally  asks  the  pur- 
chasing agent  for  a  quantity  of  "  240B,"  or 
whatever  he  has  been  using.  The  purchasing 
agent  then  finds  in  the  meantime  either  "  240B  " 
has  trebled  in  price,  or  the  producer's  plant  has 
burned,  or  he  is  unable  to  deliver  for  some 
unknown  reasons,  but  that  he  can  get  from  an- 
other producer  "  360X,"  which  he  is  assured 
is  much  better  and  may  be  cheaper.  It  is  at 
this  point  trouble  begins. 
86 


COAL-TAR  PRODUCTS 


87 


The  following  are  some  of  the  oil's  used  in  the 
flotation  process  i1 

1.  Coal-tar  Products. 

2.  Coal-tar  Cresols. 

3.  Fuel-oils. 

4.  Gas-oil  (stove-oil). 

5.  Crude-oil  Turpentine. 

6.  Pine-oils,   Wood-tar  Oils,  Fir-oils,  Wood- 
creosotes,  etc. 

Coal-tar  Products.  —  Of  the  coal-tar  products 
cresylic  and  carbolic  acids  are  the  best  known 
reagents.  Commercial  cresylic  acid  is  an  *oily 
refractive  liquid,  generally  with  a  red  or  yellow 
tinge,  has  a  specific  gravity  of  about  1.044  and 
consists  of  approximately  40  per  cent  meta- 
cresylic,  35  per  cent  orthocresylic,  and  25  per 
cent  paracresylic  acids,  the  properties  of  these 
three  isomers  being,  according  to  Lunge  and 
Keane:2 


Acid. 

Boiling-point. 

Solubility  of 
100  parts  water 
at  ordinary 
temperature. 

Orthocresvlic                

Decrees. 

191 

Volumes. 

2  $0 

Metacresylic              

203 

0.53 

Paracresylic  .         

202 

1.80 

This  acid  is  much  less  soluble  in  water  than  its 
homologue,  carbolic  acid,  and  is  still  more  easily 
broken  down  by  sulphuric,  which  probably  ac- 

1  "Oils  Used  in  the  Flotation  Process, "  by  An  Occa- 
sional Contributor,  Min.  &  Sci.  Press,  May  1,  1915. 

2  "Technical  Methods  of  Chemical  Analysis,"  1911. 


88  OIL  AND  OTHER  REAGENTS 

counts  for  the  statement  that  sulphuric  acid  may 
not  be  used  along  with  either  of  these  weaker 
acids. 

Coal-tar  Cresols.  —  Cresylic  acid  should  be 
handled  carefully,  as  it  gives  rise  to  painful 
skin  wounds,  and  may  easily  flash  into  the 
operator's  eyes.  It  is  well  to  keep  a  bottle  of 
olive  oil  handy  as  a  remedy. 

Cresylic  acid  is  an  expensive  reagent,  costing 
at  least  $1.25  per  gallon  delivered  at  western 
American  mills  in  time  of  peace.  It  comes 
principally  from  Germany  and  England.  Crude 
coal-tar  creosote,  which  is  a  by-product  of  gas- 
works, blast  furnaces,  and  gas  producers  has 
shown  some  promise  as  a  substitute. 

Carbolic  acid  (phenol)  is  a  homologue  of 
cresylic  acid.  It  is  difficult  to  distinguish  be- 
tween them,  the  smell  and  color  being  so  much 
alike.  Carbolic  acid  is  easily  broken  down  by 
H2S04,  yielding  oxalic  acid.  It  appears  to  be 
much  less  selective  than  cresylic  acid  in  its 
action  on  metallic  sulphides,  and  a  slight  ex- 
cess brings  over  a  concentrate  high  in  insoluble 
matter. 

Fuel-oils.  —  Fuel-oils  from  various  localities 
have  widely  different  action  on  any  given  ore. 
They  are  not  highly  selective  like  cresylic  acid, 
pine-oils,  etc.,  but  are  strongly  emulsive;  they 
serve  the  purpose  of  giving  body  and  mineral- 
carrying  power  to  the  relatively  weak  but  more 
selective  froths;  they  are  cheap,  quickly  ob- 
tainable, and  when  used  in  moderation  bring 
over  a  little  gangue. 


THE   PURPOSE  OF  OIL  IN   FLOTATION      89 

Gas-oils.  —  Gas-oil,  or  stove-oil,  a  distillation 
product  of  crude  oil,  is  a  strong  emulsifying 
agent,  which  is  at  times  most  useful.  It  must 
be  used  in  very  small  quantities. 

Crude-wood  Turpentine.  —  This  is  a  dark 
reddish-brown  liquid  with  a  pungent  smell. 
On  gravity-flow  machines  it  is  of  little  use,  as  its 
action  in  slight  excess  is  to  bring  over  gangue 
freely.  As  an  emulsifier  fuel-oil  or  tar-oil  are 
preferable.  On  machines  through  which  the 
flow  of  pulp  is  maintained  by  mechanical  means, 
it  has  been  found  a  valuable  reagent  for  the 
purpose  of  controlling  the  levels  of  pulp,  through 
its  physical  action  on  the  froth. 

Pine-oils,  wood-tar  oils,  fir-oils,  wood-creo- 
sotes, etc.,  are  the  products  resulting  in  a 
destructive  distillation  of  soft  wood. 

The  Purpose  of  Oil  in  Flotation.  —  The  exact 
function  of  oil  in  flotation  is  a  point  that  has 
not  yet  been  settled,  although-  it  seems  ob- 
vious enough  that  we  want  oil  for  two  main 
purposes:1  1st,  to  furnish  a  film  around  the 
particle,  and,  2d,  to  act  as  a  means  ol  making  a 
foam  or  froth. 

Oils  may  be  roughly  divided  into  two  classes: 
1.  Collectors  or  Oilers;  2.  Frothers  or  Foamers. 

Oils  that  are  good  "  collectors  "  are  practi- 
cally insoluble  in  water  and  form  a  film  not 
easily  evaporated,  so  make  persistent  bubbles.2 

1  "How  Flotation  Works,"  by  G.   D.   Van  Arsdale, 
Eng.  &  Min.  Jr.,  May  13,  1916. 

2  "  Universal  Flotation  Theory, "  by  C.  T.  Durell,  Mex- 
ican Min.  Jr.,  July,  1916. 


90  OIL  AND   OTHER  REAGENTS 

Good  "  frothers  "  are  oils  more  or  less  soluble 
and,  while  they  make  quantities  of  bubbles  and 
much  froth,  evaporate  quickly,  so  that  the 
bubbles  burst  more  readily. 

The  Qualities  of  a  Flotation  Oil.  —  G.  D.  Van 
Arsdale  states  t1 

I  think  it  is  safe  to  say  that  we  want,  first, 
an  oil  whose  viscosity  is  such  as  to  enable  it  to  be 
finely  divided  or  extended;  second,  that  it 
should  not  emulsify  readily;  third,  that  its 
physical  qualities  should  be  such  that  the 
resultant  of  the  interfacial  tensions  between 
water,  oil,  and  particle  should  be  such  as  to 
cause  with  certainty  the  entrance  of  a  mineral 
particle  into  it  and  the  exclusion  of  a  gangue 
particle. " 

The  object  in  the  addition  of  a  minute  amount 
of,  for  example,  pine-oil  is  to  change  the  surface 
tension  and  contact  angle  of  the  other  oil  or  of 
a  particle  coated  by  it  so  as  to  enable  it  now  to 
float,  which  it  otherwise  would  not  do.  Heat 
apparently  acts  in  the  same  way,  for  if  we  drop 
some  oil  on  the  surface  of  hot  water,  it  does  not 
film  out  but  assumes  the  globular  form. 

It  would  seem  that  when  two  oils  are  used, 
one  for  its  filming  effect  and  the  other  as  a 
frother,  they  should  be  used  separately  in  the 
apparatus,  first  using  the  filming  oil,  thus  ob- 
taining a  maximum  filming-out  condition,  then 
followed  by  the  frother. 

In  general,  pine-oil  makes  a  brittle  froth,  which 
immediately  dies;  creosotes  make  a  more  elastic 
froth,  the  bubbles  of  which  may  expand  to  3 
1  "How  Flotation  Works,"  Mexican  Min.  Jr.,  July,  1916. 


THE  QUALITIES  OF  A  FLOTATION  OIL     91 

inches  in  diameter  or  more  before  rupture. 
Coal-tar  products  are  poor  frothing  agents  and 
if  used  must  be  aided  by  either  creosote  or  pine- 
oil  to  produce  a  good  froth  and  insure  a  high 
recovery.  Oils  of  a  lubricating  nature  seem  to  be 
of  little  value  in  flotation,  while  such  light  oils 
as  gasoline  and  naphtha  are  of  value  only  for 
thinning  the  heavy  coal  and  wood-tars.  On 
some  ores  crude  pine-tar  will  in  itself  combine 
both  the  properties  of  frothing  and  collecting. 
On  others,  this  may  have  to  be  enriched  by  the 
addition  of  some  one  of  its  more  volatile  constit- 
uents such  as  refined  pine-oil,  turpentine,  or 
wood-creosote. 

The  following  examples  will  illustrate  how 
oils  are  mixed  to  give  a  good  flotation  oil.  At 
the  Inspiration,  for  instance,  the  mixture  is  80 
per  cent  crude  coal-tar,  20  per  cent  coal-tar 
creosote;  at  another  plant  on  similar  oil  45  per 
cent  El  Paso  coal-tar,  40  per  cent  coal-tar 
creosote,  10  per  cent  cresol,  and  5  per  cent  pine- 
oil;  at  the  Daily- Judge  mine  40  per  cent  crude 
coal-tar,  40  per  cent  creosote,  and  20  per  cent 
pine-oil;  in  the  Coeur-d'Alene  on  zinc  ore 
straight  wood-creosote  was  used;  on  the  National 
Copper  ore  plain  turpentine  will  work  but  pine- 
oil  will  work  better. 

In  the  above  examples  at  the  Inspiration,  1^ 
to  2  Ib.  of  the  mixture  are  used  per  ton  of  ore; 
at  the  Daily- Judge,  1  to  1J  Ib;  and  at  the 
National  T3^  Ib.  oil  is  sufficient.  "  The  proper 
kind  or  kinds  of  oil  and  quantity  required  can 
only  be  determined  at  present  by  tentative 


92  OIL  AND  OTHER  REAGENTS 

experiments;  so  far  no  scientific  short-cut  is 
known. " 

The  trend  of  work  to-day  seems  to  be  to  study 
flotation  from  the  standpoint  of  the  ore,  its 
electrostatic  charge  (so-called),  etc.,  and  from 
the  standpoint  of  colloidal  chemistry  it  is  be- 
lieved that,  in  addition,  a  study  of  oils  would 
give  a  better  understanding  of  the  process  and  of 
the  variables  concerned,  while  also  aiding  in 
the  solution  of  certain  theories  not  yet  advanced.1 

Froth  and  Bubbles.  —  The  idea  has  been 
abandoned  by  most  people  that  a  low  surface 
tension  is  the  essential  requirement  for  froth 
formation.  As  mentioned  by  Coghill  in  a 
recent  writing,2  "  contamination  of  the  liquid 
with  an  impurity  that  will  cause  a  variable  sur- 
face tension  is  the  real  requirement." 

A  bubble  of  air  is  spherical  in  shape,  and  this 
shape  can  only  be  maintained  if  the  external 
pressure  exceeds  the  internal  pressure.  Since 
a  bubble  does  not  expand  per  se,  large  bubbles 
can  only  be  accounted  for  by  heat,  coalescence, 
or  electrification.  Viscosity  is  an  important 
factor  in  froth  persistence,  as  it  increases  the 
tendency  of  the  liquid  film  and  thus  prevents 
ready  rupture.  The  rupture  or  bursting  of 
bubbles  is  explained  thus: 3 

1.   Concussion  upon  a  surface  film  deficient  in 

1  "Oils  for  Flotation,"  by  Chas.  Y.  Clayton  and  C.  E. 
Peterson,  Min.  &  Sci.  Press,  April  22,  1916. 

2  "  The  Science  of  a  Froth,"  Min.  &  Sci.  Press,  February 
26,  1916. 

3  "The  Flotation  of  Minerals,"  by  Robt.  J.  Anderson, 
Min.  &  Sci.  Press,  July  8,  1916. 


FROTHS  FORMED  BY  FLOTATION  OILS      93 

the    requisite    viscosity    and    variable    surface 
tension. 

2.  Relief  of  pressure  —  here  the  gas  of  the 
bubble  in  expanding  exerts  a  pressure  exceeding 
that  of  the  liquid  film. 

3.  Adhesive  force  of  the  entrained  gas  for  the 
atmospheric  air. 

4.  Evaporation  of  the  liquid  film. 
Flotation  bubbles  will  burst  for  any  one  or  a 

combination  of  these  reasons. 

Furthermore  i1 

(a)  Frothing  never  occurs  in  pure  liquids  and 
is  a  definite  proof  that  the  solute  or  dispersed 
phase  lowers  tne  surface  tension  of  the  solvent. 

(6)  A  froth  which  shows  adsorption  at  the 
interfacial  boundary  of  solution  and  gas  de- 
pends for  its  persistence  on  the  production  of  a 
viscous  film  at  that  boundary. 

(c)  These  viscous  films  are  the  direct  result 
of  surface  adsorption  of  the  dispersed  phase, 
that  is,  dissolved  contaminant,  the  amount  of 
which  is  small  —  disappearingly  so. 

The  work  of  Hall  and  Miss  Benson  shows  that 
in  a  foaming  liquid  the  foam  is  richer  in  the 
dissolved  contaminant  than  in  the  bulk  of  the 
liquid. 

Froths  Formed  by  Flotation  Oils.2  —  The  froth 
produced  by  various  oils  differs  with  the  ma- 
chine in  which  it  is  made.  For  instance,  in  the 

1  "The  Flotation  of  Minerals,"  by  Robt.  J.  Anderson, 
Min.  &  Sci.  Press,  July  8,  1916. 

2  " Froths  Formed  by  Flotation  Oils,"  by  William  A. 
Mueller,  Eng.  &  Min.  Jr.,  July  1,  1916. 


94  OIL  AND  OTHER  REAGENTS 

Minerals  Separation  type  of  machine,  where  the 
froth  rides  in  the  spitzkasten  for  some  time 
before  leaving  it,  there  is  plenty  of  time  to  col- 
lect and  mat  together,  and  in  this  case  the  froth 
always  lies  in  a  "  dead  "  state,  only  coming  off 
as  it  is  forced  out  by  other  froth  from  the  rear. 
In  this  case  the  froth  loses  its  characteristics  so 
far  as  the  bubble  itself  is  concerned. 

In  the  Callow  type  of  machine  the  froth  is 
always  in  rapid  motion  and  no  dead  froth  ac- 
cumulates. It  is  kept  overflowing  by  the  con- 
stantly rising  bubble  column  formed.  In  the 
Cole-Bergmann  and  Flynn-Towne  types  of  ma- 
chines the  froth  acts  as  in  the  Callow  type.  In 
these  two,  however,  a  deeper  froth  column  is 
carried  and  this  makes  a  slight  difference  in 
the  froth,  making  the  bubbles  slightly  smaller. 

In  adding  oils  for  flotation  it  is  of  the  utmost 
importance  that  they  be  well  mixed  with  the 
pulp  before  flotation  is  attempted.  This  is 
usually  done  by  adding  the  oils  in  the  mills 
during  grinding,  and  this  is  the  most  desirable 
method.  Sometimes  where  this  cannot  be  done, 
as  is  the  case  where  primary  slimes  are  treated  by 
flotation  and  the  oils  are  not  wanted  in  the  rest 
of  the  feed,  a  Pachuca  tank  is  used  for  the 
mixing.  This  works  fairly  well,  although  it  is 
not  the  most  desirable  way  of  mixing  where  the 
entire  pulp  is  to  be  treated.  If  not  thoroughly 
mixed,  the  oils  kill  froth  rather  than  produce 
any.  When  a  machine  is  in  good  working  order 
and  some  raw  oil  suddenly  gets  into  the  pulp, 
the  froth  immediately  seems  to  dissolve,  leaving 


FROTHS  FORMED   BY  FLOTATION  OILS      95 

the  pulp  showing  through  the  froth.  In  these 
cases  the  froth  rushes  back  and  forth  in  the 
machine;  the  bubbles  become  very  brittle  and 
finally  disappear. 

Another  important  feature  in  adding  the  flo- 
tation oils  is  that  they  be  fed  in  some  continu- 
ous way  and  not  spasmodically,  since  the  latter , 
would  entail  constant  attention  at  the  machine 
and  abnormal  conditions  at  all  times.  There 
are  several  devices  for  uniform  oil  addition.  One 
is  by  a  pump  in  which  the  stroke  of  the  piston 
can  be  varied,  thus  giving  any  desired  amount 
of  oil,  from  a  drop  at  a  time  to  a  steady  stream. 
Another  satisfactory  device  is  a  method  whereby 
the  oil  is  taken  from  the  rim  of  a  wheel  which 
operates  so  that  the  rim  passes  through  oil 
contained  in  a  reservoir.  A  piece  of  flat  metal 
is  then  fixed  by  a  set  screw  and  spring  to  rest 
against  the  rim.  By  adjustment  of  the  screw 
the  piece  of  metal  can  be  shifted  across  the  rim 
so  as  to  take  in  a  greater  or  less  area,  thereby 
increasing  or  diminishing  the  oil  flow.  Still  a 
third  method  consists  of  a  small  bucket  or  two 
on  an  endless  chain  passing  over  a  pulley,  much 
the  same  as  a  bucket  pump,  located  above  the 
launder  where  the  oils  are  to  be  added  and  an- 
other pulley  in  a  barrel  or  drum  containing  the 
oil  mixture  below.  The  bucket  carries  its  small 
amount  of  oil  up,  discharges  into  the  launder,  and 
is  refilled  again  on  passing  through  the  barrel, 
etc. 

In  making  any  changes  in  increasing  or  de- 
creasing the  amount  of  oil  or  adding  different 


96  OIL  AND  OTHER  REAGENTS 

kinds  of  oil,  make  them  very  gradually.  In 
increasing  or  diminishing,  especially,  be  careful 
and  only  change  the  rate  very  slowly,  allowing 
enough  time  to  give  the  change  a  chance  to  show 
up  in  the  machine.  Especially  is  this  important 
when  the  oils  are  added  in  "the  mills,  as  it  takes 
some  time  for  a  change  in  oil  to  make  its  ap- 
pearance, since  it  is  diluted  to  such  an  extent 
and  worked  over  such  a  comparatively  large 
volume. 

The  froth  characteristics  here  described  apply 
to  live  froths  such  as  are  formed  in  the  air  types 
of  machines.  The  agitator  type,  with  the  ex- 
ception of  the  agitator-and-air  type  com- 
bined, usually  has  a  spitzkasten  or  settling  com- 
partment in  which  the  froth  congeals  and  so 
loses  its  bubble  characteristics.  In  these  ma- 
chines the  froth  characteristics  are  not  so 
noticeable. 

Characteristics  of  Pine-oil 

Pine-oil,  as  a  general  rule,  is  a  rather  poor 
mineral  collector,  but  a  good  frothing  agent. 
For  this  reason  it  is  generally  used  only  as  a 
frother,  although  there  are  some  cases  where  it 
will  take  the  place  of  a  mineral  collector  as  well 
as  the  frothing  agent.  Its  action  is  delicate, 
and  at  plants  where  pine-oil  is  largely  used  the 
machines  will  require  much  closer  attention. 
For  instance,  it  is  a  good  mineral  collector  on 
ores  carrying  chalcocite  and  on  some  zinc  ores. 
A  pine-oil  froth,  in  addition  to  being  brittle,  is 
also  watery  and  at  times,  when  there  is  too  much 


CHARACTERISTICS  OF  PINE-OIL          97 

of  it  present,  it  tends  to  make  a  dirty  froth  and 
low-grade  concentrate.  When  present  in  these 
large  amounts,  the  concentrate  froth  will  often 
carry  large  particles  of  silica  and  gangue  ma- 
terial; that  is,  some  that  will  pass  28-mesh  and 
stay  on  a  60-mesh  screen.  The  froth,  however, 
does  not  toughen  up  because  of  its  excess  oiling, 
and  in  this  way  pine-oil  differs  from  most  others. 
The  froth  will  be  dirty,  as  is  the  case  with  other 
oils,  and  cannot  be  cleaned,  but  the  latter  is  due 
largely  to  excess  froth  rather  than  to  the  tough- 
ness of  the  froth,  as  is  the  case  with  other  oils. 
By  the  addition  of  acid,  or  sometimes  a  caustic, 
its  action  as  a  mineral  collector  can  often  be 
increased,  but  it  still  retains  the  same  charac- 
teristics of  brittleness  and  delicacy. 

Next  to  pine-oil  the  most  important  flotation 
agent  is  coal-tar.  As  a  general  rule  the  coal- 
tars  are  too  stiff  and  thick  to  be  used  by  them- 
selves and  so  must  often  be  diluted  with  some 
other  oil,  preferably  one  in  its  own  class.  The 
oils  commonly  used  for  this  purpose  are  coal- 
tar  creosote,  cresol,  and  other  coal-tar  products. 
Sometimes,  however,  wood-creosote,  fuel-oil,  or 
others  are  used. 

Coal-tar  is  a  poor  frothing  agent,  but  a  good 
mineral  collector,  and  it  is  seldom  used  without 
mixing  with  some  pine-oil  or  other  frothing 
agent.  The  bubbles  from  coal-tar  itself  are  also 
brittle,  but  in  the  presence  of  mineral  it  often 
seems  to  become  tougher,  the  mineral  and  oil 
film  apparently  mating  together.  The  froth 
from  this  oil  is  always  mineralized  to  a  high 


98  OIL  AND  OTHER  REAGENTS 

degree  when  it  is  mineralized  at  all.  Coal-tar, 
with  a  suitable  frothing  agent,  is  adapted  to 
almost  any  ore.  By  this  statement  I  mean 
that  it  is  not  adapted  to  any  one  mineral,  but 
works  as  a  rule  with  the  minerals  of  copper, 
zinc,  and  some  others.  The  froth  does  not 
acquire  any  great  depth  unless  some  other  oil  is 
mixed  with  it.  For  this  reason  we  seldom  see  a 
straight  coal-tar  froth  except  in  an  experimental 
machine.  Coal-tar  is  hard  to  mix  with  the  pulp, 
and  it  cannot  be  done  well  except  by  grind- 
ing. I  have  seen  coal-tar,  even  when  mixed 
with  pine-oil,  separate  when  reaching  the  ma- 
chine, although  in  this  case  it  had  been  added  in 
a  Pachuca  tank  at  the  head  of  the  machine. 
When  coal-tar  shows  up  in  the  machine  as  raw 
oil,  it  hag  not  the  strong  froth-killing  power  of 
the  other  oils,  but  lies  on  the  froth  in  flakes, 
sometimes  deadening  the  froth  in  the  immediate 
vicinity  and  at  other  times  seeming  to  mate 
the  small  bubbles  together,  forming  a  sort  of 
hole  in  the  froth,  toward*  which  the  bubbles  in 
the  vicinity  have  a  strong  tendency  to  rush.  Ar- 
riving, they  seem  to  be  swallowed  up  much  as 
a  cork  will  act  when  thrown  into  a  whirlpool. 
Raw  coal-tar  in  the  machine  is  not  so  detrimental 
as  the  other  oils,  but,  nevertheless,  it  should  be 
avoided.  When  in  great  excess,  coal-tar  has  a 
strong  tendency  to  separate,  as  has  been  noted, 
even  when  apparently  well  mixed.  Even  though 
it  has  no  strong  frothing  power,  when  too  much 
is  used  it  will  cause  some  excess  frothing  and 
a  dirty  froth,  though  not  so  easily  as  other  oils. 


COAL-TAR  CREOSOTE  99 

Coal-tar  Creosote 

Coal-tar  creosote  is  used  mostly  as  a  dilutant 
for  the  cheaper  coal-tar  oil,  and  for  this  purpose 
it  is  very  good.  The  creosote  bubble  has  a 
tendency  to  be  rather  large,  ranging  in  size 
from  about  an  inch  in  diameter  to  as  much  as 
12  in.  and  sometimes  even  more.  The  bubble 
has  a  tendency  to  be  tenacious.  It  is  very 
tough  and  in  breaking,  the  bubbles  tend  to  ex- 
pand rather  than  be  destroyed  altogether.  With 
two  bubbles  side  by  side,  the  breaking  seems  to 
take  place  in  the  film  uniting  them,  so  that 
where  there  were  two  bubbles  at  first,  there  is 
only  one  after  ^bursting.  This  enlarging  of  the 
bubble,  of  course,  has  its  limit,  and  we  seldom 
see  them  much  over  12  in.  in  diameter  unless 
there  is  a  great  excess  of  creosote,  when  they 
may  get  to  be  of  such  size  as  to  reach  across  the 
machine.  On  bursting,  the  mineral  burden  is 
drawn  by  the  film  to  the  film  of  the  neighboring 
bubbles  with  which  they  were  in  contact  before 
bursting.  The  bubble  has  good  carrying  capac- 
ity for  mineral.  When  too  much  oil  is  present, 
however,  there  is  the  same  tendency  to  carry 
gangue,  and  this  is  usually  at  the  expense  of  the 
mineral.  The  oil  mixes  rather  easily,  the  action 
in  the  Pachuca  tank  being  sufficient,  although 
mixing  in  the  grinding  mills  is  at  all  times  to  be 
recommended. 


100  OIL  AND  OTHER  REAGENTS 

Wood-creosote  Bubbles 

Wood-creosote  has  some  of  the  same  charac- 
teristics of  the  coal-tar  creosote,  but  differs 
widely  in  others.  The  toughness  of  its  bubbles 
is  even  more  marked.  The  size  of  the  bubble  is 
also  somewhat  different.  The  two  oils  are  not 
interchangeable  —  that  is,'  the  one  cannot  be  used 
as  a  substitute  for  the  other,  as  coal-tar  creosote 
seems  to  work  better  on  copper-bearing  ores 
than  the  wood-creosote  and  the  latter  seems  to 
work  better  on  zinc  ores.  Wood-creosote  is  often 
used  as  a  dilutant  for  coal-tar  in  the  flotation 
of  zinc  ores.  The  size  of  bubbles  varies  greatly. 
The  characteristic  froth  shows  small  ones  re- 
sembling the  pine-oil  bubble,  together  with  the 
larger  ones.  The  froth,  like  that  of  coal-tar 
creosote,  is  tough,  and  a  small  excess  of  oil  makes 
a  dirty  and  voluminous  froth  that  is  hard  to 
break  up.  The  bubble  varies  from  this  type 
when  an  excess  of  oil  is  used,  tending  to  become 
larger  and  more  elastic. 

Turpentine  is  not  used  so  much  at  the  present 
time  as  when  flotation  first  appeared  in  this 
country.  The  turpentine  froth  is  persistent 
and  elastic.  It  has  a  tendency  to  hold  every- 
thing that  comes  in  contact  with  it,  and  for  this 
reason  it  was  formerly  used  to  bring  up  the  mid- 
dlings and  was  added  after  the  concentrates  were 
taken  off.  For  this  purpose  it  was  good,  but 
the  froth  is  so  tough  that  it  is  hard  to  break 
down,  so  that  cleaning  it  is  difficult.  Usually 
the  middling  produced  by  means  of  the  turpen- 


CRESOL,   ORJ  CRESYLIC  ACID,          101 

tine  could  not  be  cleaned  to  any  appreciable 
extent.  The  turpentine  bubble  ranges  in  size 
from  J  in.  to  2  or  3  in.  in  diameter. 

Cresol,  or  Cresylic  Acid 

Cresol,  or  cresylic  acid,  formerly  was  the 
chief  flotation  agent  used  in  the  flotation  of  cop- 
per minerals,  but  its  use  is  now  limited  to  small 
proportions  in  the  mixtures  with  coal-tar.  The 
cresol  bubble  is  of  medium  size  —  that  is,  from 
^  to  2  and  3  in.  in  diameter  —  and  as  a  rule  the 
bubble  is  not  too  brittle  and  not  too  tough,  but 
makes  a  good  froth  to  handle.  The  nature  of 
the  oil,  however,  made  it  disagreeable  to  handle 
and  also  somewhat  dangerous;  this,  together 
with  the  bringing  out  of  coal-tar  and  the  ad- 
vance in  price  of  cresol,  gradually  brought  it 
to  a  point  where  only  a  comparatively  small 
amount  is  now  used. 

The  oil  was  a  good  frothing  agent  as  well  as  a 
good  mineral  collector,  and  its  use  was  almost 
universal  a  short  time  ago.  The  froth  is  rather 
easy  to  break  down,  and  for  this  reason  the  con- 
centrate produced  is  rather  easily  cleaned.  The 
oil  is  very  slightly  soluble  in  water  and  mixes 
rather  easily.  Violent  agitation,  as  in  a  Pa- 
chuca  tank  or  in  the  Minerals  Separation  type 
of  machine,  is  often  enough  to  give  good  dis- 
tribution and  a  good  flotation  froth. 

The  froth  produced  by  fuel-oil  is  of  the  same 
appearance  as  that  of  coal-tar  creosote  as  far 
as  the  bubbles  are  concerned,  which  are  nearly 
the  same  size,  ranging  from  2  to  4  and  6  in.  in 


102  OIL  AND  OTHER  REAGENTS 

diameter.  The  froth,  however,  is  very  brittle 
when  the  right  amount  of  oil  is  used  and  is  much 
cleaner  than  the  creosote.  In  fact,  the  froth  is 
almost  too  clean,  so  that  a  clean  tailing  is  hard 
to  make  with  fuel-oil  alone.  Mixed  with  some 
oil  like  creosote,  however,  it  sometimes  does 
good  work.  The  concentrates  from  the  prelimi- 
nary treatment  often  need  no  further  treatment. 
Where  a  final  product  is  made  as  concentrate, 
the  tailings  are  usually  retreated,  and  in  this 
case  the  creosote  effects  seem  to  carry  through 
to  the  other  treatment,  while  the  fuel  often  has 
to  be  added  in  the  second  treatment.  Various 
ores  differ  slightly  on  this  point.  Again,  a 
little  fuel-oil  in  a  coal-tar-creosote  mixture  will 
sometimes  aid  in  cleaning  the  froth. 

When  the  fuel-oil  is  in  excess,  the  froth  pro- 
duced is  stringy  and  the  bubbles  often  get  to  be 
of  such  size  as  to  stretch  across  the  machine. 
I  have  seen  them  over  2  ft.  in  length.  The 
froth  under  these  conditions  is  also  dirty  and 
will  pass  through  a  cleaner  with  practically  no 
better  grade  being  produced  than  before  enter- 
ing. Acid  is  sometimes  an  aid  in  the  use  of  fuel- 
oil,  especially  when  the  oil  is  in  excess.  The 
froth  from  excess  fuel-oil  is  hard  to  break  down. 

Pine-tar  oil  is  coming  into  the  limelight  more 
just  now  as  a  possible  flotation  agent  for  copper 
carbonates,  but  I  doubt  whether  it  will  be  use- 
ful alone.  It  is  stiff  and  flows  poorly,  so  that 
it  must  be  mixed  with  some  other  oils  in  order 
to  make  it  of  such  viscosity  as  to  flow  so  that  it 
may  be  added  steadily  and  slowly. 


DEALERS  IN  FLOTATION  OILS  103 

The  froth  resembles  that  from  wood-creosote 
and  pine-oil  in  appearance  of  the  bubbles,  but  in 
texture  it  is  very  much  more  fine-grained  than 
the  wood-creosote  It  is  a  powerful  frothing 
agent  similar  to  pine-oil.  It  is  easy  to  flood 
the  plant  with  froth  from  this  oil.  The  froth 
is  characterized  by  being  dirty,  but,  like  pine- 
oil,  is  capable  of  holding  up  considerable  coarse 
mineral  as  well  as  gangue.  When  a  flood  of  this 
froth  reaches  the  cleaner,  it  is  subjected  to  very 
little  cleaning,  owing  to  its  frothing  character. 
Often  the  addition  of  a  small  amount  of  fuel-oil 
will  tend  to  make  a  cleaner  froth,  but  with  the 
pine-tar  oil  a  very  clean  froth  must  not  be  ex- 
pected except  at  the  cost  of  high  tailings. 

Oleic  acid  is  used  at  several  plants  in  this 
country  and  *is  confined  mostly  to  zinc  ores. 
The  size  of  bubbles  varies  with  the  amount  of 
oil  used,  but  ranging  from  several  inches  to  a 
foot  in  diameter.  The  froth  is  very  persistent 
and  stringy,  and  the  bubble  film  is  often  strong 
enough  to  support  light  objects. 

Eucalyptus-oil  is  used  mostly  in  Australia, 
although  a  small  amount  of  it  may  be  encoun- 
tered in  this  country  at  times.  Its  cost,  how- 
ever, is  very  much  against  it  here. 

Dealers  in  Flotation  Oils.1  —  The  following  is 
a  list  of  dealers  in  different  oils  who  have  placed 
on  the  market  various  products.  A  host  of 
these  dealers  are  prepared  to  supply  these  prod- 
ucts at  any  time,  of  fairly  uniform  quality. 

1  "Flotation-oils,"  by  O.  C.  Ralston,  Min.  &  Sci. 
Press,  June  10,  1916. 


104  OIL  AND  OTHER  REAGENTS 

None  of  them  has  been  able  to  exactly  dupli- 
cate their  car-load  shipments,  so  that  the  general 
practice  is  to  test  each  shipment  of  oil  in  a 
laboratory  testing  device  to  determine  the  proper 
method  of  using  a  given  shipment  of  oil.  This 
non-uniformity  of  shipments  will  doubtless  van- 
ish when  the  market  becomes  steady. 


Dealers  in  Flotation  Oils 

Wood-oils 

Pine-oils,  Resin-oils,  Wood-creosotes,  Tar-oils, 
Turpentines,  etc. 

1.  Pensacola  Tar  &  Turpentine  Co.,  Gull  Point,  Fla. 

2.  General  Naval  Stores  Co.,  New  York. 

3.  Georgia  Pine  &  Turpentine  Co.,  158  Perry  St.,  New 

York. 

4.  Central  Distilling  Co.,  Helena,  Ark. 

5.  United  Naval  Stores  Co.,  New  York. 

6.  American  Tar  &  Turpentine  Co.,  New  Orleans,  La. 

7.  Cleveland  Cliffs  Iron  Co.,  Cleveland,  Ohio. 

8.  Chesapeake  Tar  &  Rosin  Co.,  Baltimore,  Md. 

9.  Custer  City  Chemical  Co.,  Custer  City,  Pa. 

10.  Yaryan  Naval  Stores  Co.,  Brunswick,  Ga. 

11.  Hussay  &  O'Connel,  Savannah,  Ga. 

12.  Florida  Wood  Products  Co.,  Jacksonville,  Fla. 

13.  Oregon  Wood  Distilling  Co.,  Portland,  Ore. 

14.  National  Wood  Products  Co.,  Wilmington,  N.  C. 

15.  Chapman  Manufacturing  Co.,  Savannah,  Ga. 

16.  Spiritine  Chemical  Co.,  Wilmington,  N.  C. 

Eucalyptus-oil 

17.  Atkins,  Kroll  &  Co.,  San  Francisco,  Cal.,  and  other 

importers. 


DEALERS  IN  FLOTATION  OILS    105 

Coal-tar,  Coal-creosotes,  and  Aromatic 
Hydro-carbons. 

1.  The  Barrett  Co.,  New  York. 

2.  F.  J.  Lewis  Manufacturing  Co.,  Chicago,  111. 

3.  American  Creosoting  Co.,  New  Orleans,  La. 

4.  American  Tar  Products  Co.,  Chicago,  111.,  and  St. 

Louis,  Mo. 

5.  Republic    Creosoting    Co.,    Indianapolis,    Ind.,    and 

Minneapolis,  Minn. 

6.  American  Coal  Refining  Co.,  Denver,  Colo. 

7.  Numerous  by-product  coke-ovens,  such  as: 

Pennsylvania  Steel  Co.,  Steelton,  Pa. 

National  Tube  Co.,  Penwood,  W.  Va. 

Milwaukee  Coke  &  Gas  Co.,  Milwaukee,  Wis. 

Pennsylvania  Steel  Co.,  Lebanon,  Pa. 

Solvay  Process  Co.,  Syracuse,  N.  Y. 

By-products  Coke  Corporation,  South  Chicago,  111. 

Semet-Solvay  Co.,  Detroit,  Mich. 

Central  Irpn  &  Coal  Co.,  Tuscaloosa,  Ala. 

New  England  Gas  &  Coke  Co.,  Everett,  Mass. 

Illinois  Steel  Co.,  Joliet,  111. 

Maryland  Steel  Co.,  Sparrows  Point,  Md. 

8.  Numerous  municipal  and  similar  coal-gas  plants. 


Vegetal  Oils 

1.  Cottonseed-oil,  etc.,  Southern    Cottonseed  Oil    Co., 

New  York. 

2.  Corn-oil,  Corn  Products  Co.,  New  York. 

3.  Palm-oil,  Peter  van  Schaack  &  Co.,  Chicago,  111. 


Animal  Oils  (Fatty  Acids) 

1.  Oleic  acid,  Peter  van  Schaack  &  Co.,  Chicago,  111. 

2.  Oil-flotation  grease  emulsion,  Mohawk  Refining  Co., 

Cleveland,  Ohio. 


V 

106  OIL  AND   OTHER   REAGENTS 

PETROLEUM   PRODUCTS 

Crude  j  Asphaltum  Base 

1.  California  crude: 

Union  Oil  Co.,  Santa  Paula,  Cal. 
Associated  Oil  Co.,  Los  Angeles,  Cal. 
Standard  Oil  Co.,  Richmond,  Cal. 

2.  Road  oil  No.  80,  Harris  Oil  Co.,  Los  Angeles,  Cal. 

Reconstructed  Petroleum  Oils 

1.  Special  mineral  separator,  Continental  Oil  Co.,  Salt 

Lake  City,  Utah. 

2.  Solulene  and  minolene,   Star  Lubricating  Co.,   Salt 

Lake  City,  Utah. 

Refined  Petroleum  Products 

1.  Stove-oil,  Standard  Oil  Co.,  San  Francisco,  Cal. 

2.  Stanolind,  etc.,  Continental  Oil  Co.,  Salt  Lake  City, 

Utah. 

3.  Flotation-oils,  Utah  Oil  Refining  Co.,  Salt  Lake  City, 

Utah. 

4.  Heavy  mineral  flotation-oils,  Geo.  P.  Jones  &  Co., 

St.  Louis,  Mo; 

.    5.   Refinery  acid  sludge,  any  refinery. 
6.   Lubricating  oils,  any  company. 

Special  Mixtures  of  Mineral  and  Wool  Oils 

1.  Calol-oils,  Standard  Oil  Co.,  Richmond,  Cal. 

2.  Mine  &  Smelter  Supply  Co.,  Denver,  Colo. 

3.  Hendrie  &  Bolthoff   Manufacturing  &  Supply  Co., 

Denver,  Colo. 

The  costs  of  flotation-oils  have  varied  so  much, 
owing  to  the  unsettled  market,  that  it  is  almost 
impossible  to  give  an  idea  of  what  they  should 
cost.  For  a  rough  estimate  it  is  possible  to  say 


PETROLEUM   PRODUCTS  107 

that  crude  petroleum  will  cost  the  same  as  for 
other  purposes.  Many  of  the  specialized  prod- 
ucts, such  as  coal-tar,  listed  above,  will  cost 
about  5^  or  less  per  gallon.  The  coal-creosotes 
and  the  wood-creosotes  cost  15  to  30f£  per  gallon; 
the  pine-oils  45  to  60^,  and  eucalyptus-oil  will 
cost  $1.50  or  more  per  gallon.  The  effect  of 
the  ending  of  the  war  as  regards  coal-tar  and 
creosote  in  the  American  market  is  uncertain, 
but,  so  far  as  known,  wood  products  will  not 
be  affected,  and  petroleum  products  for  flo- 
tation will  almost  certainly  be  little  affected. 
Flotation  men  do  not  like  to  have  their  oil  costs 
go  over  5j£  per  ton  of  slime  treated,  and 
many  costs  are  nearer  to  2^  or  possibly  even 
less. 

There  can  be  no  doubt  that  the  higher-grade 
pine-oils  and  ather  wood-oils  are  the  best  adapted 
to  general  flotation  work,  but  the  question  of 
what  is  commercially  feasible  is  entirely  different. 
Thus  the  wood-creosotes  are  meeting  with  much 
favor.  Many  of  the  special  petroleum  products, 
especially  those  high  in  sulphur,  are  adaptable 
for  rough  concentration  of  copper  ores,  but  the 
most  favored  materials  for  such  ores  at  present 
seem  to  be  the  coal-tar  products  in  combination 
with  topped  crude  petroleum,  oils  from  which  the 
lighter  fractions  have  been  removed  by  distil- 
lation. Coal-tars  and  creosotes,  with  a  small 
addition  of  pine-oils,  are  being  used  a  great  deal 
in  zinc  work,  and  the  wood  creosotes  find  favor 
in  the  treatment  of  galena  ores.  Gold  and 
silver  ores  seem  to  require  much  pine-oil,  al- 


108  OIL  AND  OTHER  REAGENTS 

though  the  pine-oil  can  be  diluted  with  some  of 
the  coal-creosote  oils. 

It  will  be  found  that  there  is  a  considerable 
number  of  oils  that  will  give  good  results  on 
any  given  ore,  if  the  mechanical  treatment  is 
adjusted  to  suit  each  given  oil. 

Following  is  a  table  showing  the  amount  of 
flotation-oils  being  consumed  every  month 
throughout  the  United  States.  These  figures 
were  collected  at  the  beginning  of  1916  by  direct 
communication  with  the  companies. 


PETROLEUM   PRODUCTS 


109 


1 


•a 

d 


31 

1? 

.2   a 

1  I? 
.2   8 


•o 

d 
& 


lO  CO      •  *O 
t^«  CO      •  !>• 


5  O  CO  O5 


coco 


58 


§ 


g 


§S 


05 

'  oT 


I 


5  O 

;& 


o 

<M 


l 


1 


CHAPTER  VI 
TESTS 

The    Important    Points    to    Test  f or.  —  The 

amount  of  work  required,  in  testing  any  given  ore 
for  the  flotation  process,  is  considerable,  since 
the  proper  kind  or  kinds  of  oil  and  quantity  and 
amount  of  other  reagents,  acid  or  alkali,  can 
only  be  determined  at  present  by  tentative 
experiment;  so  far  no  scientific  short-cut  is 
known. 

The  most  important  points  to  be  tested  on  a 
given  ore  with  any  given  flotation  machine  are: 

1.  Method  of  Grinding. 

2.  Fineness  of  Grinding. 

3.  Kind  of  Frothing  Agent  Used. 

4.  Amount  of  Frothing  Agent. 

5.  Temperature. 

6.  Acidity  or  Alkalinity. 

7.  The  Effect  of  Varying  the  Speed  of  Agi- 
tation when  Mechanical  Agitation  is  Used. 

8.  Necessity  of  Preliminary  Agitation. 

9.  Effect  of  Addition  Agents  in  Flocculating 
Gangue-slime. 

Preliminary  Considerations.  —  It  may  be  seen 
that  there  may  be  a  certain  best  combination  of 
the  above  variables;  hence  the  desirability  of 
doing  the  tests  in  a  small  laboratory  machine 
where  many  trials  can  be  made  in  a  short  time. 
110 


PRELIMINARY  CONSIDERATIONS        111 

In  attacking  refractory  ores  there  are  a  num- 
ber of  ingenious  things  that  can  be  done  to  the 
pulp  both  in  and  out  of  the  machine.  The 
trouble  may  be  due  to  deleterious  substances, 
which  sometimes  can  be: 

1.  Washed  out. 

2.  Rendered  harmless  by  boiling. 

3.  Overcome  by  acidifying. 

4.  Met  with  by  making   alkaline  with  lime 
before  entering  the  machine. 

5.  Occasionally,  the  ore  will  not  work  well 
under  ordinary  conditions,  but  will  yield  beauti- 
fully after  fine  grinding. 

6.  Sometimes  extra  reagents  are  necessary, 
such  as  powdered  charcoal,  modified  oils,  argol, 
soap,  calcium,  sulphate,  alum,  etc. 

One  can  see  that  a  rational  method  of  de- 
vising the  proper  tests  in  such  cases  must  be 
based  on  some  theory  of  flotation.  Colloid 
chemistry  is  -e  branch  of  knowledge  that  will 
aid  in  the  intelligent  control  of  such  tests. 

After  the  best  conditions  have  seemingly  been 
established,  they  should  be  further  tried  in  a 
larger-sized  machine  before  they  are  incorpo- 
rated into  the  general  practice  of  a  mill  for 
laboratory  results  are  somewhat  pessimistic  as  • 
compared  to  large  scale  work. 

Again  when  a  good  set  of  conditions  has  been 
found  for  flotation  treatment  of  an  ore,  it  is 
best  to  recover  the  water  from  each  test  to  see 
what  effect  a  closed  circuit  of  the  mill  water  will 
have.  Some  oil  and  chemicals  are  thus  re- 
covered, cutting  down  the  amounts  necessary 


112  TESTS 

for  operation.  In  fact,  a  carboy  or  two  of  the 
water  to  be  used  in  the  large  mill  should  be 
used  to  make  certain  that  no  deleterious  con- 
tamination will  issue  from  this  source. 

Oil  samples  for  test  purposes  can  be  obtained 
from  the  various  wood-distilling  companies  now 
advertising  in  the  Technical  Press,  from  gas 
companies,  and  from  petroleum-refining  com- 
panies. 

Finally,  it  is  well  to  be  prodigal  in  the  amount 
of  analytical  work  connected  with  flotation 
testing  in  order  to  discover  interesting  differ- 
ences in  gangue  constituents  carried  into  the 
concentrate,  as  well  as  to  find  the  best  conditions 
for  leaving  out  some  gangue  constituent  that  is 
less  desirable  than  the  rest.  If  an  experimenter 
does  his  own  analytical  work  he  can  be  expected 
to  spend  three-fourths  of  his  time  analyzing 
what  has  been  done  the  other  fourth. 

Method  of  Grinding.  —  As  a  rule  laboratory 
machinery  for  the  pulverization  of  an  ore  is  of 
the  dry-grinding  type,  with  the  exception  of 
small  ball-mills  that  can  crush  from  1-  to  100- 
Ib.  charges  in  the  wet.  Consequently,  most 
people  start  with  weighed  charges  of  finely- 
ground  dry  ore,  a  known  quantity  of  water,  of 
oil,  and  of  acid  or  alkali.  Generally  most  dry- 
ground  ore  must  be  treated  in  an  acidified  pulp 
to  get  good  flotation.  Doubtless,  the  surfaces 
of  sulphide  particles  become  somewhat  oxidized 
in,  or  shortly  after,  dry  grinding,  and  the  func- 
tion of  the  acid  would  be  to  clean  the  slightly 
oxidized  surfaces.  Wet  grinding  usually  does 


METHOD  OF  GRINDING  113 

not  call  for  so  much  acid.  In  nearly  all  labora- 
tory work  finer  grinding  than  is  used  in  practice 
seems  to  be  necessary.  This  is  probably  due  to 
the  smaller  amounts  of  froth  that  are  formed. 
Such  small  quantities  of  froth  cannot  form  layers 
as  deep  as  those  made  in  the  large  machines. 
60  mesh  is  about  the  maximum  size  that  can  be 
floated  with  any  chance  of  getting  high  recovery, 
while  ore  crushed  somewhat  finer  than  this  gives 
much  more  ease  and  expedition  in  operation. 
Wet  grinding  is  more  desirable,  as  it  parallels 
conditions  in  practice,  where  most  of  the  fine 
grinding  of  ore  is  in  Chilian,  tube,  or  other  mills. 
However,  wet  grinding  is  much  harder  to  ma- 
nipulate in  a  small  laboratory  and  requires  more 
time.  The  dry  weight  of  the  feed  to  the  flotation 
machine  must  be  known;  hence  a  weighed  charge 
of  dry  ore  crushed  to  10  mesh  can  be  introduced 
into  a  porcelain  or  iron  pebble-mill  for  fine 
grinding  and  ground  for  a  length  of  time  found' 
necessary  to  reduce  the  pulp  to  sufficient  fineness 
—  15  minutes  to  24  hours.  The  charge  can  be 
poured  and  washed  through  a  coarse  screen 
(to  retain  the  bubbles)  into  a  bucket  and  thence 
into  a  flotation  machine.  The  oxidation  of 
sulphide  surfaces  is  thus  avoided,  but  separate 
grinding  of  each  charge,  in  order  to  know  its 
exact  weight,  is  rather  tedious  and  requires  a 
number  of  small  mills  if  many  tests  are  to  be 
run  (Fig.  15)  on  account  of  slow  speed  in  grind- 
ing. A  mill  with  iron  balls  rather  than  pebbles 
is  of  greater  service.  It  is  possible  to  introduce 
the  flotation  oil  before  grinding,  to  be  sure  that 


114 


TESTS 


FINENESS  OF  GRINDING 


115 


it  will  be  thoroughly  mixed.  For  thick  viscous 
oils  this  is  highly  beneficial,  as  a  ball  mill  gives 
about  the  best  conditions  'for  agitation  and 
mixing.  Usually  1-  to  2-lb.  charges  are  used 
and  a  small  laboratory  mill  of  the  Abb6  type 


J4  in  bolt 


FIG.  16. 


serves  well,  although  a  good  mill  can  be  made 
with  a  10-in..,  length,  8-in.  iron  pipe,  and  two 
heavy  iron  caps  for  same  (Fig.  16). 

Fineness  of  Grinding.  —  This  would  depend  to 
some  extent  upon  the  character  of  the  ore.  The 
valuable  mineral  may  be  completely  liberated 
at  fairly  coarse  meshes,  but  it  has  been  found 
from  experience  that  60-mesh  material  is  often 
hard  to  float  with  any  chance  of  getting  a  high 
extraction,  while  the  operation  is  performed 
with  much  more  ease  and  expedition  when  the 
ore  is  crushed  somewhat  finer.  Some  experimen- 
ters have  claimed  that  they  were  able  to  float 
even  as  large  as  30-mesh  material. 


116  TESTS 

Kind  of  Frothing  Agent  Used.  —  An  oil  may 
give  a  very  good  percentage  of  extraction  on  one 
ore,  whereas  it  will  be  an  absolute  failure  when 
used  on  another,  although  both  ores  chosen  are 
very  adaptable  to  the  flotation  process. 

In  some  cases  a  single  oil  will  have  both  the 
properties  of  frothing  and  collecting,  but  usu- 
ally a  good  frother  is  not  a  collecting  oil,  so 
that  in  most  cases  a  combination  of  two  or  more 
oils  is  necessary  to  give  good  results  in  the  re- 
covery. 

Amount  of  Frothing  Agent.  —  In  testing  for 
the  efficiency  of  a  given  oil,  it  is  advisable  to 
tabulate  the  results  obtained  with  varying  per- 
centages of  this  oil;  and  it  is  best  to  start  with 
about,  0.01  per  cent  of  oil  in  the  solution,  then 
increasing  the  oil  in  each  successive  experiment 
by  about  0.02  per  cent. 

The  following  forms  are  convenient  for  the 
tabulation  of  results: 


AMOUNT  OF   FROTHING  AGENT         117 


H 
CO 


o 


I 


sg 


of  ai 
ol.  to  c 
weigh 


31 


118  TESTS 

To  show  the  effect  of  variation  in  quantity.     Pine-oil. 


Charge. 

Variable, 
grams. 

Derived  data. 

Froth. 

Assay  of  con. 

**  0* 

*! 

Zn 

Pb 

Ore,  grams  
Water,  grams  .  .  . 
Acid,  H2SO4  .... 
Oil,  H2SO4 

400 
1200 
2.0 
Variable 
65 
2000 
7 

0.5 
1.0 
1.5 
2.0 

29.0 

38.0 
37.0 
51.0 

53.2 
43.1 
42.4 
28.6 

74.6 
79.2 
75.8 
70,0 

Temp,  in  °  C.  .  .  . 
Speed,  r.p.m.  .  .  . 
Time,  minutes  .  . 

EFFICIENCY   CURVE 

Efficiency  of  pine-oil  in  terms  of  frothy  assay  and,  ex- 
traction. 


Per  cent  _-?l»°  in  Irofli 

1    1 

-60 
50 
10 

\c 

5  drani  Oi 

J 

1.0  JGra 

nO 

11 

nn 

fl\ 

>Gr 

anu 

Oil 

Of) 

y 

2G 

ran 

sO 

1 

10 

' 

Q    10   20  80  40  50   60   70  80 


Per  cent  extraction.    Zinc . 


Acidity  or  Alkalinity.  —  The  amount  of  acid 
or  alkali  required  requires  the  same  manipulation 
as  with  oils.  The  following  are  some  of  the 
probable  effects  of  acid: 

1.  Prevents  emulsification. 

2.  Prevents  deflocculation. 

3.  Diminishes  surface  tension  of  the  liquid. 


SPEED  OF  AGITATION  119 

4.  Diminishes  the  gas-liquid  contact  angle. 

5.  Increases  the  viscosity  of   the  gas-liquid 
surface. 

6.  From    the    standpoint    of    the    electrical 
theory    sulphuric    acid    (as   electrolyte)    would 
play  a  prominent  part. 

7.  Removes  surface  oxidation  and  may  con- 
tribute in  the  addition  of  bubbles. 

The  Effect  of  Temperature.  —  In  many  cases 
heat  is  required  and  in  some  cases  to  a  high 
degree.  For  laboratory  work  solutions  are  best 
heated  by  introducing  steam,  generated  in  a 
suitable  vessel. 

Speed  of  Agitation.  —  Many  reports  of  flo- 
tation test-work  with  mechanical-agitation  ma- 
chines gives  the  speed  of  the  rotation  of  the 
agitating  paddles.  In  most  flotation  labora- 
tories it  is  possible  to  get  much  the  same  work 
done  with  quite  a  variation  of  speeds,  the  only 
effect  being  to  lengthen  or  shorten  the  time  of 
treatment.  It « seems  that  the  importance  of 
this  matter  is  somewhat  exaggerated.  Some 
means  of  speed  control  is  necessary  and  the 
speed  can  be  adjusted  in  each  case  until  the  froth 
presents  the  proper  appearance  as  to  depth, 
size  of  bubbles,  color,  etc.  Speeding  toward 
the  end  of  the  test  is  good  practice,  as  it  gives 
a  deeper  froth  with  a  faint  line  of  concentrate 
on  the  top.  The  speed  is  better  adjusted,  for 
each  test,  to  suit  the  conditions,  rather  than 
running  a  series  of  tests  with  different  speeds. 
Only  in  the  slide  machine,  where  operation  of 
the  impeller  must  be  suspended  in  order  to 


120 


TESTS 


allow  froth  to  collect,  is  the  speed  of  much  im- 
portance. 

In  connection  with  the  electrical  theory, 
Thomas  M.  Bains,  Jr.,  states:1 

The  amount  of  electrification  of  the  bubble 
will  depend  on  various  conditions,  such,  for  ex- 
ample, as  the  amount  of  friction  produced  by 
the  blades  of  a  Minerals  Separation  machine. 
Increase  the  speed  and  the  electrification  is 
greater  and  the  attraction  for  conductors  will 
increase,  reducing  the  proportion  of  conduc- 
tivities in  the  tailing.  Referring  to  D.  G. 
Campbell's  article  in  the  Mining  &  Engineering 
World  of  January  17,  1914,  the  speed  of  agi- 
tation and  the  percentage  of  extraction  is  given 
as  follows: 


Speed  of  blades,  r.p.m. 

Extraction, 
per  cent. 

Weight  of  prod- 
uct, grams. 

1800                  

68 

39 

1200  

54 

32 

900 

46 

26 

600 

39 

18 

The  extraction  seems  to  vary  directly  as  the 
square  root  of  the  increase  in  speed.  But  it 
will  be  observed  that  in  the  increased  extraction, 
the  percentage  of  sulphide  in  the  concentrate 
decreases,  due  to  the  extraction  of  the  small 
particles  of  mixed  gangue  and  sulphide.  If  the 
bubbles  are  highly  charged,  the  concentrate  will 
not  be  as  clean  in  a  particular  case  as  if  they 
were  less  charged. 

Effect  of  Addition  Agents  in  Flocculating 
Gangue-slime.  —  The  froth  of  a  flotation  ma- 

1  Min.  &  Sti.  Press,  November  27,  1915. 


FLOCCULATING  GANGUE-SLIME        121 

chine,  when  viewed  in  a  glass  window  in  the 
side  of  the  machine,  has  the  appearance  of 
coagules  of  sulphide,  as  though  the  oil  or  other 
agent  has  flocculated  the  sulphides.  The  gangue, 
to  sink  away  from  the  froth  quickly,  should  also 
be  flocculated.  While  acids,  alkalis,  and  other 
addition  agents  may  have  other  functions,  they 
can  easily  have  a  coagulating  effect  on  portions 
of  the  ore.  A  clean  flotation  concentrate  when 
the  gangue  is  very  colloidal  is  hard  to  obtain 
and  some  method  of  coagulating  the  slimes  of 
the  gangue  is  necessary. 

The  following  table,  "Effect  of  Addition 
Agents "  as  outlined  by  0.  C.  Ralston  is  of 
interest.1 

TABLE  H.    EFFECT  OF  ADDITION  AGENTS 

Inorganic  Electrolytes: 

Sodium  chloride  is  rarely  an  effective  addition  agent 
for  either  flocculation  or  deflocculation  of  various  slimes, 
and  when  added  to  water  to  any  extent  demanded  by  the 
ore,  is  likely  to  increase  the  viscosity  so  that  the  particles 
will  settle  slowly  in  any  case. 

Ferrous  sulphate,  the  copperas  of  commerce,  is  a  fairly 
efficient  flocculating  agent  for  negatively-charged  parti- 
cles by  virtue  of  the  fact  that  the  heavy  bivalent  ion  of 
iron  is  strongly  absorbed  by  the  colloid  particles.  It  is 
a  deflocculator  of  positively-charged  particles  under  some 
conditions. 

Zinc  sulphate,  copper  sulphate,  magnesium  sulphate, 
magnesium  chloride,  calcium  chloride,  etc.,  act  in  the  same 
way  as  iron  sulphate.  Magnesium  and  calcium  chlorides 
are  being  used  for  flocculating  slimes  in  the  overflow 
water  of  many  German  ore-dressing  plants. 

Alum  and  other  aluminum  and  ferric  salts  containing 
1  Engineering  &  Mining  Jr.,  June  3,  1916. 


122  TESTS 

trivalent  positive  ions  are  often  tremendously  effective  in 
the  flocculation  of  negative  ore  particles. 

Sulphuric  acid  and  hydrochloric  acid  are  often  effective 
coagulants  of  negative  colloids  owing  to  the  hydrogen 
ions. 

Sodium  hydroxide  is  a  most  effective  deflocculator  of 
negative  colloid  owing  to  the  strong  adsorption  of  the 
hydroxyl  ions.  It  will  flocculate  positive  colloids,  owing 
to  the  same  cause. 

Sodium  carbonate,  owing  to  its  alkaline  reaction,  will 
generally  react  in  the  same  way  as  sodium  hydrate. 

Sodium  Silicate: 

This  salt  hydrolyzes  into  sodium  hydrate  and  colloidal 
silicic  acid,  which  carries  a  negative  charge.  Both  of 
these  products  will  tend  to  disperse  or  deflocculate  a  nega- 
tively-charged ore  slime,  and  hence  sodium  silicate  is  one 
of  the  most  effective  agents  of  this  kind,  although  its  full 
effect  is  felt  rather  slowly. 

Lime: 

The  bivalent  calcium  ion  is  more  strongly  adsorbed 
than  the  hydroxyl  ions  and  hence  lime  usually  coagulates 
colloids  negatively.  It  is  widely  used  for  that  purpose 
in  cyanide  mills.  Its  effect  is  the  opposite  of  that  of 
sodium  hydrate,  in  which  the  hydroxyl  ion  is  predomi- 
nant. The  adsorbed  ions  have  been  found  to  be  carried 
down  with  the  precipitated  colloids,  as  has  been  shown 
by  any  number  of  experimenters. 

Organic  Electrolytes: 

As  mentioned  in  the  body  of  the  article,  these  sub- 
stances react  in  many  diverse  ways.  Citric  acid  and 
oxalic  acid  and  their  sodium  salts  have  been  found  to 
deflocculate  most  ores.  Acid  tartrates  are  said  to  slowly 
flocculate  the  negatively-charged  slime  particles.  This 
field  has  been  almost  untouched  by  metallurgists. 

Organic  Colloids  and  Semicolloids : 

Tannin  seems  to  deflocculate  nearly  all  ore  colloids  and 
is  known  to  affect  clays  in  the  same  way.  Inorganic 


MISCELLANEOUS  123 

electrolytes  in  sufficient  amounts  will  reflocculate  the 
slimes  so  treated  with  tannin,  but  the  colloids  have 
been  protected  by  the  tannin  so  that  these  electro- 
lytes are  less  effective  than  on  the  untreated  ore. 
It  produces  its  maximum  effect  after  standing 
several  hours.  It  is  very  deleterious  in  flotation, 
although  its  solutions  foam  well. 

Saponin,  the  substance  used  to  make  beer  foam, 
has  an  effect  similar  to  tannin. 

Albumen,  from  the  white  of  an  egg,  is  more  or 
less  indifferent,  but  tends  to  deflocculate  most  ore 
slimes. 

Ox  blood,  which  contains  albumin  among  other 
things,  is  a  strong  deflocculator  and  its  effects  are 
very  hard  to  counteract. 

Soap  is  an  effective  flocculating  agent  with  many 
negative  slimes,  giving  large  fast-settling  flocks. 

Glue  tends  to  flocculate  most  ore  slimes  effi- 
ciently, especially  in  the  presence  of  electrolytes, 
and  is  known  to  be  bad  for  flotation. 

Gelatin  is  also  an  excellent  flocculator. 

Starch  has  not  been  experimented  with,  but  the 
good  effect  of  flour  at  Miami  is  probably  due  to 
starch. 

Any  of  the  foregoing  colloids  can  be  salted  out 
by  electrolytes  and  thereby  cause  flocculation  of 
the  ore  slimes  in  which  the  process  takes  place. 

Miscellaneous.  —  The  measuring  and 
testing  of  flotation-oils  in  the  laboratory 
have  been  more  or  less  exact.  It  is  com- 
mon practice  to  count  the  number  of  drops 
of  oil  falling  from  a  small  piece  of  glass 
tubing.  A  Mohr  pipette1  of  1  cc.  total 
capacity  for  measurement  of  the  amount 

1  "  Testing  Ores  for  the  Flotation  Process,  II," 
O.  C.  Ralston  &  Glen  L.  Allen,  Min.  &  Sd.  Press, 
January  8,  1916. 


124  TESTS 

of  oil  used  in  each  test  is  very  convenient. 
Such  a  pipette  is  shown  in  Fig.  17.  It  will 
be  seen  that  this  pipette  allows  measurement 
of  the  oil  to  the  nearest  0.01  cc.,  which  is  close 
enough  for  all  purposes.  If  the  density  of  the 
oil  is  known,  the  volume  as  measured  by  this 
method  is  quickly  converted  into  the  weight  of 
oil  used. 

In  the  article  "  Testing  Ores  for  Flotation, 
Process,  II  "  it  is  stated:1 

The  testing  of  oil  samples  for  flotative  power  is 
a  matter  that  needs  standardizing.  It  is  desirable 
to  classify  oils  according  to  flotative  power,  but 
just  how  to  do  this  is  not  exactly  clear.  A  unit 
of  "  flotativeness"  might  be  established  and  each 
oil  referred  to  that  unit  in  terms  of  percentage. 
But  it  has  to  be  remembered  that  the  best  oil 
for  one  ore  may  not  prove  to  be  the  best  oil  for 
another,  although  two  such  series  of  oils  might 
roughly  parallel  each  other.  For  any  given  ore, 
it  would  be  permissible  to  make  such  a  measure- 
ment on  a  series  of  oils  and  group  them  according 
to  some  definite  standard.  A  standard  oil  might 
be  chosen,  and  the  value  of  a  second  oil  expressed 
in  percentages  of  the  flotative  power  of  the  first, 
as  determined  by  using  equal  quantities  of  the 
two  oils  in  tests  on  an  ore  under  identical  con- 
ditions. This  test  could  not  be  fair  for  the 
reason  that  different  amounts  of  two  different 
oils  are  necessary  to  accomplish  the  same  results. 
Further,  the  conditions  of  acidity  or  alkalinity 
might  favor  one  oil  and  handicap  another.  If 
we  measured  the  amount  of  oil  necessary  to  give 
a  fixed  percentage  of  extraction,  the  first  of  the 

1  "Testing  Ores  for  the  Flotation  Process,  II,  "  O.  C.  Ral- 
ston &  Glen  L.  Allen,  Min.  &  Sci.  Press,  January  8, 1916. 


DISPOSAL  OF  THE  FROTH  125 

above  objections  would  be  satisfied,  but  condi- 
tions of  acidity  or  alkalinity  could  make  the  test 
unfair  for  some  oils.  Hence  the  dilemma  as  to  a 
standardized  test  of  a  flotation-oil. 

No  single  test  could  definitely  place  an  oil  in 
any  scheme  of  classification,  and  nothing  can  be 
done  but  run  a  series  of  tests,  using  varying 
amounts  of  the  oil  to  be  tested  with  varying 
acidity  or  alkalinity.  The  temperature  of  the 
pulp  must  be  kept  constant,  although  it  has  a 
minor  effect. 

Considerable  work  has  been  done  along  this 
line  at  the  Missouri  School  of  Mines  and  Metal- 
lurgy.1 Their  work  has  been  for  the  purpose  of 
investigating  the  properties  or  combination  of 
properties  that  make  oils  valuable  as  flotation 
agents.  They  have  suggested  many  points 
worthy  of  investigation. 

Disposal  of  the  Froth.  —  The  handling  of  the 
flotation  froth  in  the  laboratory  finds  diffi- 
culties which  are  reflected  in  practice.  It  is 
often  very  slow  to  settle  and  filters  with  diffi- 
culty. A  vacuum  filter,  connected  with  a 
laboratory  aspirating  pump,  is  a  very  convenient 
method  of  getting  the  concentrate  out  of  the 
froth.  A  large  porcelain  Biichner  funnel  fitted 
into  a  filtering  flask,  as  is  shown  in  Fig.  23,  is 
found  to  be  very  convenient.  A  copper  vacuum 
filter  is  of  much  the  same  type,  provided  with 
a  porous  false  bottom  of  acid-proof  wire-cloth, 
resting  on  a  punch  plate,  as  shown  in  Fig.  32, 
of  the  Callow  test  set.  Such  a  filter  can  be 

1  "Oils  for  Flotation,"  by  Chas.  Y.  Clayton  and  C.E. 
Peterson,  Min.  &  Sci.  Press,  April  22,  1916. 


126  TESTS 

placed  under  the  froth  discharge  of  a  flotation 
machine  so  that  a  fairly  dry  cake  of  the  con- 
centrate is  ready  for  further  drying  at  the  end  of 
the  flotation  test.  By  loosening  the  outer  rim 
of  filter  paper  and  then  turning  the  funnel  up- 
side down  over  a  pan,  the  filter-paper  with  the 
concentrate  can  be  dropped  into  the  dry-pan 
by  gently  blowing  into  the  stem  of  the  funnel. 
This  is  set  aside  in  a  warm  place  to  dry  and  later 
weighed  against  a  filter-paper  tear.  After 
weighing  a  numbered  tag  is  put  in  each  pan 
along  with  the  cake. 

The  products  coming  from  the  flotation  ma- 
chine should  be  watched  closely  and  occasionally 
panned  or  examined  with  the  microscope  to  see 
what  kind  of  work  is  being  done.  This  is  fairly 
easy  to  determine  as  the  sulphides  are  most  of 
them  distinguished  easily  from  the  gangue  under 
the  microscope,  and  likewise  gangue  particles 
in  the  froth  concentrate  can  often  be  dis- 
tinguished. A  microscope  is  a  most  useful  ad- 
junct in  a  flotation  laboratory. 

Types  of  Machines  and  Their  Operation 

Flotation-test  apparatus  must  necessarily  be 
classified  in  the  same  way  as  large-scale  ma- 
chines, namely:  (a)  film-flotation  machines, 
(6)  acid-flotation  machines  and  (c)  froth  ma- 
chines of  both  pneumatic  and  mechanically 
agitated  types. 

Film  Flotation,  as  exemplified  in  the  Mac- 
quisten  l  and  in  the  Wood  machines,  does  not 
i  Min.  &  Sd.  Press,  Vol.  XCVI,  p.  414  (1908). 


FILM   FLOTATION 


127 


seem  to  have  the  same  wide  application  as  does 
froth  flotation;  hence  little  need  be  said  about 
them. 

Macquisten  tubes  have  such  a  small  capacity 
that  a  single  tube  is  small  enough  for  test-work 
on  a  few  pounds  of  ore  at  a  time  (Fig.  18).  A 


-Feed 


—Concentrate 


Tailing 


*  FIG.  18. 

small  4-ft.  tube  is  known  to  give  trustworthy 
results,  although  a  larger  one  is  more  desirable. 
The  Wood  machine  can  be  built  in  miniature 
and  for  several  years  a  small  machine  of  the 
type  shown  in  Fig.  19  has  been  used  in  the 
plant  of  the  Wood  Ore-testing  Works  at  Denver.1 
This  machine  was  about  2  ft.  long  and  1  ft. 

1  H.   E.   Wood,    Trans.   A.I.M.E.,    Vol.    XLIV,    pp. 
684-701  (1912). 


128 


TESTS 


wide.  The  method  of  operation  is  the  same  as 
that  of  a  full-sized  machine.  As  neither  of 
these  machines  has  been  much  used  in  practice, 


FIG.  19. 

they  are  merely  mentioned  for  the  sake  of  com- 
pleteness.    Hoover l   has   recommended   a   test 
on  a  vanning  plaque  so  that  the  sulphides  will 
1  "  Concentrating  Ores  by  Flotation." 


FILM   FLOTATION 


129 


float  off  onto  the  surface  of  the  water,  but  this 
method  is  not  practical  and  Hoover  has  given  it 
merely  as  a  test  to  illustrate  the  film  processes. 
In  testing  ores  for  the  Potter  and  the  Delprat 
processes  Hoover  gives  an  illustrative  test-tube 
experiment.  (See  Fig.  20.)  Tubes  containing 
3  per  cent  H2S04  or  acid  salt-cake  solutions  and 


FIG.  20. 

a  little  sulphide  ore  are  warmed  nearly  to  the 
boiling  temperature.  Bubbles  of  C02  attach 
themselves  to  the  sulphide,  travel  to  the  sur- 
face of  the  solution,  discharge  into  the  air,  and 
drop  the  Sulphide  into  the  pocket  on  the  under- 
side of  the  tube,  as  shown  in  the  sketch.  In 
another  test  a  200-cc.  beaker  is  used  with  100  cc. 
of  3  per  cent  H2S04  and  brought  to  nearly 
boiling  temperature.  The  ore  when  intro- 
duced into  this  yields  a  froth  composed  of 
sulphides  supported  by  bubbles  of  C02.  In  case 
the  ore  is  deficient  in  carbonate,  an  addition  of 
as  much  as  3  per  cent  of  calcite  or  siderite  is 
made.  The  froth  is  skimmed  with  a  spoon  as 
soon  as  it  forms.  The  results  obtained  with 


130 


TESTS 


these  tubes  are,  however,  not  reliable  as  a  great 
deal  of  the  mineral  is  often  lifted  partly  but 
never  reaches  the  surface;  consequently  ex- 
tractions are  low.  A  better  test  machine  is  the 
small  unit  shown  in  Fig.  21. 

The   acid   should   be   allowed   to   run   down 
through  a  section  of  garden  hose  to  within  an  inch 


Garden  Hose 


Wooden  Paddle 


Froth 


FIG.  21. 

of  the  surface  of  the  ore  and  the  ore  should  be 
kept  stirred  with  a  wooden  paddle  so  that  the 
bubbles  of  C02  generated  by  the  action  of  the 
acid  can  lift  the  sulphides  out  of  the  body  of  the 
pulp.  The  froth  formed  should  be  skimmed  with 
the  paddle  as  fast  as  made,  then  filtered,  dried, 
weighed,  and  analyzed.  Not  many  ores  yield 
gracefully  to  this  treatment  as  slimes  give  poor 
extractions.  Fines  and  Wilfley-table  middlings 
are  better  adapted,  and  the  presence  of  siderite 
in  the  pulp  is  desirable,  as  it  reacts  slowly  with 


MECHANICAL  FROTHING  131 

dilute  acid.  From  1  to  3  per  cent  of  H2S04  is 
best  in  testing  and  \  to  \\  per  cent  solutions  on 
the  large  scale  will  give  about  the  same  results. 
The  temperature  of  the  pulp  should  be  main- 
tained at  70°  C.  by  use  of  a  steam  jet.  The 
extractions  obtained  are  always  lower  than  in 
full-sized  units.  While  it  is  not  necessary  in 
this  process,  it  will  greatly  assist  in  the  flotation, 
and  the  addition  of  a  small  amount  is  often  of 
much  assistance  in  test-work. 

Mechanical  Frothing.  —  This  process,  as  de- 
veloped by  the  Minerals  Separation  Co.,  in 
England  and  Australia,  and  modified  by  others, 
has  been  one  of  the  most  important  methods  of 
flotation,  therefore  the  laboratory  machinery 
that  has  been  developed  is  at  as  high  a  state  of 
perfection  as  any  such  machinery  now  in  use. 

The  Janney  machine  is  probably  the  best  de- 
signed machine  for  getting  reliable  quantitative 
results  on  a  small  quantity  of  ore.  See  photo- 
graph and  sketch,  Figs.  22  and  23.  It  can  be 
seen  that  the  agitation-compartment  is  cylin- 
drical in  shape  and  that  its  top  is  surrounded 
by  a  froth-box,  which  slopes  into  a  spitzkasten, 
where  the  froth  can  be  skimmed.  The  tailing 
sinks  to  a  return-hole  at  the  bottom,  passing 
into  the  agitation-compartment  again.  To  pro- 
vide good  agitation,  four  vertical  baffles  are 
attached  to  the  wall  of  the  agitation-compart- 
ment, against  which  the  pulp  is  swirled  by  the 
two  impellers.  Lining  the  walls  with  expanded 
metal  lathing  or  with  a  coarse-mesh  iron  screen 
adds  to  the  thorough  mixing  that  the  pulp  must 


132  TESTS 

receive.  The  two  impellers  are  on  a  common 
shafting,  which  enters  the  machine  through  a 
stuffing-box  in  the  bottom  of  the  machine.  The 
lower  impeller  with  four  vertical' vans  is  sub- 
merged; it  agitates  and  emulsifies  the  pulp  with 
the  upper  impeller,  likewise,  with  four  vertical 
vans,  acts  as  a  pump  to  lift  the  pulp  and  beat 
air  into  ifc.  A  pulley  and  belt  connect  the  shaft 
with  a  variable-speed  motor. 

A  dome-shaped  lid  is  used  on  the  machine. 
A  small  hole  in  the  top  of  the  dome  allows  the 
introduction  of  oil,  acid,  water,  or  other  material 
of  the  test.  The  lid  is  so  constructed  that  it  can 
be  turned  upside-down  with  the  dome  extending 
down  into  the  froth-box,  and  in  this  position  it 
can  act  as  a  funnel.  The  dome  rests  then  on  the 
top  of  the  agitation-compartment  and  no  froth 
can  escape  into  the  froth-box.  This  allows 
a  period  of  agitation  of  the  pulp  before  the 
dome-top  is  turned  right-side  up  to  allow  aeri- 
ated  pulp  to  overflow  into  the  froth-box  and 
down  into  the  spitzkasten,  where  the  froth  can 
be  removed. 

A  discharge-plug  at  the  bottom  of  the  ma- 
chine allows  the  flushing  out  of  tailing  after 
the  test  has  been  completed.  So  careful  has 
been  the  design  of  this  test-machine  that  even 
this  discharge-plug  is  beveled  to  fit  flush  with 
the  bottom  of  the  machine  and  thus  affords  no 
dead  space  in  which  the  solids  might  settle. 

The  spitzkasten  is  long  and  narrow,  in  order 
to  permit  a  deep  froth  to  be  formed  and  to 
travel  over  as  long  a  space  as  possible,  before 


MECHANICAL  FROTHING  133 

reaching  the  discharge.  This  tends  to  allow 
more  of  the  entrained  gangue  to  settle  out  of 
a  mineral  froth.  The  sides  of  the  spitzkasten 
are  of  heavy  plate-glass,  each  fastened  to  a 
metal  frame  by  means  of  screws.  The  wrought- 
iron  shaft  projects  through  a  brass  stuffing-box 
and  is  supported  by  a  ball-bearing  beneath.  All 
the  other  metal  parts  are  of  cast  aluminum. 

The  small  variable-speed  motor  may  be  of 
either  direct-current  or  alternating-current 
type.  F.  G.  Janney  recommends  the  use  of  a 
General  Electric  shunt-wound,  direct-current 
motor  for  230  volts,  with  a  rated  speed  of  1700 
r.p.m.  and  \  h.p.  The  impeller  shaft  is  to  be 
driven  at  1900  r.p.m.  maximum  speed.  For 
speed-control  he  recommends  a  General  Elec- 
tric direct-current  field  rheostat,  with  an  ampere 
capacity  of  1.25  to  0.063  at  250  volts. 

The  operation  of  the  machine  is  as  follows: 
It  is  set  up  on  a  bench  convenient  to  the  sink 
and  to  running  water.  The  motor  is  set  up 
1  ft.  to  (Jie  rear  with  the  switch  and  rheostat 
placed  so  that  they  can  be  easily  reached  while 
standing  in  front  of  the  machine.  A  IJ-in. 
round-leather  sewing-machine  belt  is  used  for 
the  drive.  The  bearings  are  well  oiled,  the 
stuffing-box  is  properly  packed,  and  some  at- 
tention should  be  given  to  it  occasionally  in 
order  to  see  that  it  is  kept  screwed  tight  enough 
to  avoid  leakage. 

Enough  clear  water  is  run  into  the  machine 
to  barely  show  in  the  spitzkasten  and  the  mo- 
tor is  started  at  its  lowest  speed.  A  500-gm. 


134 


TESTS 


charge  of  ore  ground  to  at  least  48  mesh  is  added 
and  the   cover   placed   on  the  machine  in   its 


FIG.  22. 

inverted  position.  (See  Fig.  22.)  This  is  done 
to  allow  thorough  mixing  without  circulation  of 
the  pulp.  All  or  part  of  the  oil  and  other  re- 


MECHANICAL  FROTHING 


135 


agents  are  now  added  and  the  motor  brought 
up  to  full  speed  for  30  seconds.  The  speed  is 
again  lowered  to  the  minimum  and  the  cover 
is  turned  over  into  its  upright  position.  (See 
Fig.  23.)  The  speed  is  then  raised  and  water  is 
added  through  the  hole  in  the  top  of  the  lid 


until  the  froth  in  the  spitzkasten  is  nearly 
at  the  overflow  lip.  The  ultimate  speed  of  the 
agitator  will  depend  somewhat  upon  the  charac- 
ter of  this  froth,  as  some  oils  will  give  a  deep 
persistent  froth,  while  other  froths  are  thin  and 
brittle  and  allow  of  more  water  being  added  to 
the  machine,  as  well  as  more  violent  agitation 
in  order  to  beat  more  air  into  the  pulp.  The 


136  TESTS 

froth  may  either  be  allowed  to  flow  out  of  the 
spitzkasten  of  its  own  weight  or  skimmed  with 
a  small  wooden  paddle.  It  is  a  good  idea  to  wet 
the  glass  sides  of  the  "  spitz  "  with  water  while 
the  froth  is  rising,  so  that  none  of  the  froth  will 
stick  to  the  glass. 

The  duration  of  the  test  is  about  5  minutes 
with  an  ore  that  floats  easily,  while  other  ores 
will  require  a  considerably  longer  time  to  allow 
the  entrained  gangue  to  settle  out  of  the  froth 
before  it  is  discharged  from  the  machine.  In 
such  cases  it  is  best  to  hold  back  the  froth  until 
its  appearance  shows  it  to  be  fairly  clean.  Be- 
ginners are  likely  to  dilute  their  froth  with  too 
much  gangue.  In  a  large-sized  machine  the 
froth  can  travel  over  from  4  to  8  ft.  of  spitzkasten 
before  it  is  discharged,  while  in  this  test  ma- 
chine it  only  has  a  travel  of  about  10  in.  Con- 
sequently, the  small  machine  is  liable  to  yield 
concentrate  of  too  low  a  tenor.  The  same  ap- 
plies to  most  other  machines  for  making  tests 
on  flotation. 

The  concentrate  may  be  caught  in  a  pan  or 
on  a  filter.  After  the  test  the  machine  is  brought 
back  to  low  speed  and  the  tailing  plug  removed, 
so  that  the  tailing  can  be  caught  in  a  pan  or 
bucket  or  run  to  waste. 

If  it  is  so  desired,  this  rough  concentrate  can 
be  put  back  into  the  machine  and  treated  in  the 
same  way  as  the  original  sample,  or  the  con- 
centrates from  several  tests  combined  to  give 
enough  material  for  retreatment.  If  this  is  done 
three  products  are  made,  namely: 


MECHANICAL  FROTHING  137 

1.  A  "  rougher  "  tailing  to  waste. 

2.  A  clean  concentrate  for  shipment. 

3.  A  "  cleaner  "  tailing  or  middling  which  in 
actual  practice  is  returned  to  the  head  ma- 
chine. 

When  these  conditions  are  observed  results 
only  slightly  lower  than  those  possible  with  a 
big  machine  can  be  obtained.  A  test  can  be 
run  in  from  5  to  30  minutes  in  such  a  machine 
with  500  gm.  of  ore  in  anything  from  a  3  :  1  to 
a  5  :  1  pulp.  The  glass  sides  of  the  spitzkasten 
allow  close  observation  of  the  condition  of  the 
froth,  and  this  is  a  great  advantage  to  the  be- 
ginner. The  small  amount  of  ore  necessary  for 
a  test  is  a  matter  of  considerable  convenience 
as  fine  grinding  of  the  ore  in  the  laboratories 
is  often  irksome.  The  aluminum  casting  is 
little  corroded  by  either  acid  or  alkaline  elec- 
trolytes. The  return  of  pulp  from  the  "  spitz  " 
to  the  agitating  compartment  allows  the  material 
to  be  treated  until  all  mineral  has  been  removed 
without  ^topping  the  machine,  so  that  a  single 
treatment  yields  a  clean  tailing.  However,  a 
second  treatment  of  this  "  rougher-froth "  is 
sometimes  necessary  in  order  to  get  a  high- 
grade  concentrate.  Clean  tailings  generally 
mean  only  medium-grade  concentrates  due  to 
entrainment  of  gangue  in  the  removal  of  all  the 
mineral. 

The  stuffing-box  in  the  bottom  will  probably 
leak  if  not  watched.  However,  this  driving  of 
the  impeller  from  below,  instead  of  from  above, 
leaves  the  top  of  the  machine  free  for  the  op- 


138 


TESTS 


erator  and  is  more  convenient  in  every  way. 
This  is  of  importance  in  a  laboratory  machine 
and  will  excuse  the  use  of  a  stuffing-box.  In 
large-scale  machines  a  stuffing-box  underneath 
would  not  be  tolerated  and  the  drive  should  be 
from  above. 

The  Hoover  Machine.  —  The  so-called  Hoover 
machine  was  designed  after  a  testing  machine 
described  in  the  second  edition  of  Hoover's 
book,  being  copied  from  one  of  Lyster's  patents, 
and  has  been  much  copied  by  people  wishing  to 
make  flotation  tests.  In  general,  the  machine 


Pulp— i 


Impeller 


"•  Contracted  Spitzkaten. 

FIG.  24. 


is  not  nearly  so  convenient  for  making  tests  as 
the  Janney  machine  and  other  recent  testing 
machines  on  the  market.  Its  cost  of  construc- 
tion has  been  the  main  point  in  its  favor.  The 


THE  HOOVER   MACHINE 


139 


Janney  machine  will  cost  about  $100  while  the 
Hoover  machine  can  be  built  for  a  small  frac- 
tion of  this  amount.  In  the  agitation-compart- 
ment the  pulp  is  swirled  into  the  corners  (see 
Fig.  24)  where  it  is  well  mixed  with  air;  hence 
the  baffles  sketched  in  the  Janney  machine  are 
unnecessary.  One  objection,  however,  is  that 
unless  the  agitation-compartment  is  very  tall 
the  pulp  being  swirled  in  the  corners  has  a 
tendency  to  splash  out,  and  a  lid  similar  to  the 


FIG.  25. 


one  on  the  Janney  machine  is  desirable.  How- 
ever, it  is  difficult  to  attach  one  because  the 
sfirrer  shafting  is  in  the  way.  The  operation 
of  this  machine  is  practically  the  same  as  that 
of  the  Janney,  except  that  without  glass  sides 
on  the  spitzkasten  it  is  hard  to  get  as  clean  a  froth. 
A  charge  of  1000  to  2000  gm.  was  necessary  in 
this  machine. 


140  TESTS 

Other  modified  forms  of  the  Hoover  machine 
are  shown  in  Figs.  25  and  26. 

The  Slide  Machine.  —  This  machine  as  shown 
in  Fig.  27  was  designed  by  Hoover  and  per- 
fected by  many  others.  In  recent  practice 
it  is  motor  driven.  Many  people  favor  this 
apparatus  for  the  reason  that  they  have  had 
little  opportunity  to  use  any  other  design.  In 
this  machine  the  agitator  is  driven  from  below 
through  a  stuffing-box,  as  in  the  Janney,  with  the 
consequent  freedom  of  the  top  of  the  machine  for 
the  convenience  of  the  operator.  The  top  half 
of  the  machine  is  so  constructed  that  it  can  be 
slid  to  one  side,  cutting  off  the  froth  formed  in 
the  agitation  from  the  gangue,  which  is  allowed 
to  settle.  The  operation  consists  in  agitating 
the  oil  and  other  reagents,  then  a  period  of  quiet 
during  which  the  froth  collects  at  the  top  while 
the  gangue  sinks.  Two  windows  in  the  side 
enable  the  observer  to  see  when  the  gangue  has 
subsided  sufficiently  to  allow  the  top  half  to  be 
slid  along  the  rubber  gasket,  cutting  off  the 
froth  from  the  remainder  of  the  pulp.  The 
time  necessary  for  the  settling  of  the  gangue  is 
sufficient  for  much  of  the  •  gangue  to  separate 
from  the  froth,  leaving  only  clean  sulphides 
in  the  froth.  This  element  of  the  machine  has 
made  it  of  some  value  in  testing  flotation-oils, 
but  in  a  weak  froth  much  of  the  sulphide  mineral 
also  settles  out  and  is  lost,  so  that  the  test  re- 
sults with  this  machine  often  show  unneces- 
sarily low  extractions  and  a  high  grade  of 
concentrate.  On  the  other  hand  when  con- 


1  T  \ 

X  H.PJMotor        \ 


}4  diam.  .hol 

* 

Lead  or  Copper  Pipe       y 
i/insidediam.    -^ 


to  1  diam.  hole  for  cleaning, 
to  be  fitted  with  a  plug 


Impeller.peripherical  speed 
(1500  to  1800 


142 


TESTS 


ditions  are  adjusted  to  give  a  froth  persistent 
enough  to  hold  all  the  sulphide  mineral,  con- 
siderable gangue  is  entrained  in  the  stiff  froth. 


FIG.  27. 

Further,  after  skimming  one  froth  we  find  it 
necessary  to  add  more  water  and  start  the  ma- 
chine again  to  make  more  froth.  It  is  hard  to 
make  the  slide  machines  give  a  high  extraction 
with  only  one  agitation.  The  intermittent  char- 
acter of  such  work  and  the  time  necessary  to 
wait  while  settling  are  disadvantages  that  make 
the  Janney  or  Hoover  machines  of  greater  utility. 
The  parts  are  of  cast  aluminum  with  a  rubber 
gasket  between.  A  charge  of  500  to  1000  gm. 
of  ore  is  used. 

The  Case  Machine.  —  This  machine  consists 
of  a  single  aluminum  casting,   comprising  the 


THE  SLIDE  MACHINE  143 


FIG.  29. 


144  TESTS 

agitation  cell  and  a  spitzkasten  from  which  the 
froth  is  collected. 

The  agitation  cell  contains  a  shaft  and  im- 
peller. The  impeller  is  provided  with  four 
blades  set  at  angles  of  90  degrees.  The  steel 
shaft  is  coated  with  lead  and  the  impeller 
blades  are  made  of  aluminum  to  resist  the 
corrosive  action  of  acids. 

A  piece  of  extra  heavy  pressure  tubing  pro- 
vides for  connection  between  the  bottom  of  the 
spitz  box  and  the  agitation  cell.  (See  Fig.  29.) 
With  this  tubing  is  supplied  a  strong  pinch-cock 
for  the  regulation  of  pulp  circulation,  the 
pressure  tubing  being  easily  removed  for  cleaning 
purposes. 

The  operation  of  this  machine  is  practically 
the  same  as  that  of  the  Janney  and  the  Hoover 
type.  It  is  apparently  a  modified  Hoover  ma- 
chine, made  by  the  Denver  Fire  Clay  Company, 
Denver,  Colo. 

The  Roy  and  Titcomb  Machine.  —  This  ma- 
chine invented  and  made  by  Roy  and  Titcomb, 
Inc.,  Nogales,  Ariz.,  is  a  machine  which  is 
self-contained  (Fig.  30). 

The  cells  are  cast  in  one  piece.  This  is  a 
machine  apparently  well  suited  for  laboratory 
testing  purposes,  especially  if  power  is  not 
available.  They  are  also  made  for  motor  drive. 
A  hand-power  machine  costs  $85. 

Separatory  Funnels.  —  During  the  past  year 
an  article  on  practice  in  Mexico  l  mentioned  the 
fact  that  much  of  the  preliminary  testing  on  the 
1  Min.  &  Sci.  Press,  July  24,  1915. 


THE  CASE  MACHINE 


145 


FIG.  30. 


146 


TESTS 


ore  is  done  in  separatory  funnels  (Fig.  31)  in 
which  the  charges  of  pulp,  oil,  etc.,  were  shaken, 
after  which  the  cock  at  the 
bottom  of  the  funnel  was 
opened  and  the  tailing  run 
into  a  second  separatory  fun- 
nel for  further  flotation  tests, 
the  cock  being  closed  in  time 
to  catch  the  froth.  The  ver- 
satility of  experiment  per- 
missible with  the  use  of  such 
apparatus  is  commendable. 
Obviously,  this  arrangement 
is  open  to  the  same  objection 
as  is  the  slide  machine  except 
that  separatory  funnels  are 
simple  and  inexpensive. 

In  comparison  of  the  above 
mechanical  agitation  type  of 
laboratory  machine  the  Jan- 
ney  and  Hoover  machines  are  by  far  the  most 
useful. 

Pneumatic  Flotation.  —  Among  the  different 
pneumatic  machines,  the  Callow  test-machine  is 
the  only  one  of  laboratory  size  that  has  been 
much  developed.  It  is  merely  the  commercial 
Callow  machine  reduced  in  size.  (See  Figs.  32, 
33.)  Fig.  32  shows  the  whole  plant  in  miniature 
as  developed  in  the  laboratory  of  the  General 
Engineering  Company  in  Salt  Lake  City.  It 
consists  of  a  Pachuca  mixer,  a  roughing  cell, 
cleaning  cell,  vacuum  filter,  and  sand  pump  to 
return  middling  to  Pachuca  mixer. 


FIG.  31. 


PNEUMATIC  FLOTATION 


147 


As  seen  in  the  drawing,  the  pulp  is  mixed  with 
a  Pachuca  tank  of  small  size  overflowing  into 
the  rougher  flotation-cell.  The  tailing  from  this 
rougher  goes  to  a  sand-pump  and  is  returned 
to  the  Pachuca.  The  froth  is  treated  in  a  second 


Air  Line,  4  Ibs.  Pressure 
Pressure  Gauge 
s  from  Rougher 
nd  Cleaner  Cells. 


FIG.  32. 


and  smaller  pneumatic-flotation  unit,  giving  a 
concentrate  that  overflows  into  an  ordinary 
laboratory  vacuum-filter  actuated  by  a  water 
or  aspirating  pump.  The  tailing  from  the 
"  cleaner  cell "  consists  of  a  middling  that  like- 
wise flows  to  the  sand-pump  and  back  to  the 
Pachuca. 

A  novice  will  have  no  small  difficulty  in  oper- 
ating such  an  installation,  as  there  are  a  number 
of  things  to  be  kept  in  operation  at  the  same  time. 

The  mixture  of  ore,  water,  oil,  and  any 
other  reagent  is  fed  either  into  the  suction  of  the 
sand-pump  or  into  the  top  of  Pachuca  after  air 


148 


TESTS 


has  geen  started  into  the  various  machines. 
The  overflow  from  the  Pachuca  into  the  rougher 
cell  accumulates  until  a  nice  froth  is  coming  up 


FIG.  33. 

and  nearly  overflowing.  Then  the  tailing-dis- 
charge valve  is  gradually  opened  and  froth 
allowed  to  overflow  from  the  cell  into  the 
"  cleaner  cell."  It  is  best  to  get  most  of  the 


PNEUMATIC  FLOTATION  149 

charge  circulating  before  much  concentrate- 
froth  is  allowed  to  overflow,  the  overflow  of 
froth  being  controlled  by  the  main  air  valves 
leading  to  each  unit.  After  the  valves  into 
the  individual  wind-boxes  beneath  the  machine 
have  been  once  adjusted  they  should  never  be 
disturbed,  and  all  control  of  air  supplied  should 
be  at  the  valves  in  the  main  pipes.  When 
everything  is  going  well,  the  air-pressure  in  the 
cleaner  can  be  increased  until  concentrate-froth 
is  overflowing  into  the  vacuum  filter.  A  wooden 
paddle  to  stir  any  settled  material  in  the  flo- 
tation-cell is  of  value,  as  well  as  a  small  jet  of 
water  from  a  rubber  hose  for  washing  concentrate 
along  the  froth-launders  and  for  beating  down 
froth  when  occasional  too-violent  rushes  of 
froth  from  the  cells  take  place.  After  a  test  is 
complete  the  pulp  should  be  drained  completely 
from  all  parts  of  the  machine  while  the  air  is 
still  blowing,  so  that  solids  will  not  settle  in 
passages  or  clog  the  canvas  blanket  in  the  cells. 
Only  practice  will  allow  any  one  to  get  reliable 
results  with  this  machine.  A  watch-glass  for 
catching  and  panning  occasional  samples  of  froth 
is  another  necessary  auxiliary  to  this  equip- 
ment. The  cost  of  installing  such  a  set  of 
apparatus  is  from  $100  to  $150.  At  least  1000 
gr.  of  ore  is  required  for  a  test  and  about  30 
minutes  to  1  hour  is  spent.  It  can  be  seen  that 
nothing  but  a  finished  concentrate  and  a  tailing 
are  obtained  or  a  middling  product  may  be  left 
in  the  cleaner  cell.  This  middling  may  be 
assayed  as  such  and  calculated  into  the  con- 


150  TESTS 

centrate  and  tailing  or  its  sulphides  may  be 
panned  out  and  added  to  the  concentrate.  The 
-machine  is  said  to  give  results  closely  paralleling 
those  obtained  with  larger-scale  apparatus.  A 
source  of  supply  of  air  at  3  to  5  Ib.  per  square 
inch  is  necessary  and  the  main  valves  on  the 
air-pipe  leading  to  each  machine  should  be  some 
type  of  needle  valve  in  order  to  insure  exact 
control. 

In  connection  with  this  apparatus  a  quali- 
tative oil-tester  should  be  used.  A  good  tester 
consists  of  a  glass  tube  of  about 
2  in.  in  diameter  and  2  ft.  long 
(Fig.  34).  This  can  be  set  on 
end  and  closed  at  the  bottom 
with  a  one-hole  rubber  stopper 
through  which  passes  a  glass 
tube  into  a  small  canvas  bag. 
The  small  bubbles  of  air  coming 
through  the  canvas  are  similar 
to  those  used  in  large-scale  ma- 
chines and  can  be  observed  through  the  glass 
walls  of  the  tube.  With  some  pulp  in  the  tube, 
oils,  acids,  salts,  etc.,  may  be  added  in  very  short 
tests  until  the  proper  appearance  is  obtained. 
An  overflow  lip  is  provided  in  case  it  is  desired 
to  examine  the  mineral  in  the  froth.  A  slight 
adjustment  of  the  air  will  provide  an  ample 
overflow  of  froth. 


CHAPTER  VII 
THE  COST  OF  FLOTATION 

After  having  determined  a  satisfactory  com- 
bination of  oils,  etc.,  and  in  general  the  ore  is 
found  to  be  amenable  to  the  flotation  process, 
the  next  important  question  confronting  the 
flotation  engineer  is,  "  How  much  will  a  flo- 
tation plant  of  a  given  required  capacity  cost?" 
Or,  "How  does  the  cost  of  flotation  compare  with 
that  of  other  methods  of  concentration?"  It  is 
hard  to  obtain  any  exact  figures  that  will  apply 
in  all  cases,  but  a  few  average  and  approximate 
figures  for  some  of  the  flotation  processes  are 
given  below;  from  these  the  reader  can  be  able 
to  figure  out  for  himself  approximately  the  cost 
of  any  particular  kind  and  size  of  flotation  plant. 

For  the  Callow  or  Pneumatic  agitation  proc- 
ess, the  following  figures  are  those  given  by 
John  M.  Callow.1 

Power.  —  The  National  Copper  Co.,  which 
treats  500  tons  per  day,  requires  35  h.p.  This 
means  12.53  tons  per  horse  power,  or  1.25  kw- 
hr.  per  ton. 

A  company  which  treats  2400  tons  per  day 
requires  210  h.p.,  which  means  11.45  tons  per 
horse  power,  or  1.56  kw-hr.  per  ton. 

1  Paper  as  presented  by  him  at  annual  meeting  of 
Utah  section  of  the  A.I.M.E.,  Salt  Lake  City,  October, 
1915. 

151 


152  THE   COST   OF  FLOTATION 

The  former  company  uses  10  cells  and  the 
latter  60,  which  gives  3.5  horse  power  per  cell  in 
both  cases. 

He  gives  the  maximum  figure  as  2.5-kw-hr. 
per  ton  of  feed,  with  an  air  pressure  of  from  5 
to  5.5  lb.,  the  air  being  generated  by  a  Roots  or 
Connersville  positive  blower. 

Oil,  Labor,  and  Maintenance.  —  The  oil  costs 
from  1J  to  3£  per  pound,  and  about  1.5  lb.  of 
oil  to  the  ton  of  feed  is  used.  This  would  give 
an  average  of  2.5^  per  ton  of  feed.  The  average 
cost  of  labor  and  maintenance  would  be  about 
If  i  per  ton  of  feed. 

The  following  is  also  given  by  Mr.  Callow, 
as  being  an  average  figure  for  a  2000-ton  plant : 

Labor $0.0125 

Oil -. 0.0250 

Maintenance 0 . 0050 

Power 0.0250 

Total,  per  ton  of  feed $0.0675 

And  for  a  250-ton  plant  about  lOji  per  ton  of 
feed.  As  the  size  of  the  plant  increases,  one  can, 
of  course,  see  that  the  cost  per  ton  of  feed  will 
decrease,  and  in  one  case  a  figure  as  low  as  $0.061 
is  given. 

The  Denver  Fire  Clay  Co.,  Denver,  Colo., 
gives  the  cost  of  a  complete  flotation  plant  of 
100  tons  capacity  as  ranging  from  $1500  to 
$5000.  The  cost  of  oil,  7  to  15  i  per  ton,  cost 
of  acid  10  to  20jzS,  and  the  operation  and  main- 
tenance, from  15  to  25 i  per  ton.  From  these 
figures  the  total  cost  of  flotation  ranges  from 


OIL,  LABOR,  AND   MAINTENANCE       153 

32  to  60^  per  ton  of  ore,  in  a  process  where  both 
oil  and  acid  are  used. 

In  the  case  of  the  Potter  process,  Hoover 
gives  the  cost  per  unit  as  about  $1000,  in- 
cluding installation,  for  the  Elmore  vacuum 
machine,  about  $1750  per  unit,  a  capacity  of  a 
unit  ranging  from  30  to  50  tons  per  day. 

For  the  various  flotation  processes  in  use  at 
Broken  Hill,  we  have  an  average  figure  of  3  s. 
7  d.  or  43^  per  ton  of  ore.  This  figure  does  not 
include  the  royalty  of  1  shilling  per  ton  of  ore 
treated. 

From  recent  data  published,  the  cost  of  flo- 
tation in  a  certain  mill  is  35  £  per  ton  of  crude 
mill  feed,  or  60^  per  ton  of  actually  treated; 
whereas  in  the  same  mill  the  cyanide  process 
costs  80^  per  ton  of  crude  mill  feed,  or  $1.50 
per  ton  of  ore  actually  treated. 

At  the  mill  of  the  Consolidated  Copper  Co., 
Miami,  Ariz.,  about  14,500  tons  of  ore  are 
treated  daily  by  the  flotation  process.  Includ- 
ing royally,  the  mining  and  milling  costs  about 
$1.00  to  $1.15  per  ton  of  ore,  which  would  make 
the  c&st  of  concentration  almost  corresponding 
to  the  cost  mentioned  above. 

At  the  mill  of  the  Consolidated  Arizona 
Smelting  Co.,  Humboldt,  Ariz.,  the  cost  of 
concentration  by  flotation,  including  coarse 
crushing  and  flotation  royalty,  is  slightly  over 
$1.00  per  ton.  For  a  period  of  six  months, 
the  cost  of  flotation,  exclusive  of  royalty,  was 
27 'i  per  ton.  The  power  consumption  of  the 
flotation  machine  is  32.7  kw.  per  hour. 


154  THE  COST  OF  FLOTATION 

The  royalty  charged  by  process  owners  for 
the  use  of  their  processes  is  very  high;  Hoover 
gives  the  average  figure  as  1  shilling  or  25 j£  per 
ton  of  ore  treated.  Few  companies  are  willing 
to  pay  such  a  high  royalty  and  this  naturally 
has  been  one  of  the  chief  sources  of  trouble. 

Judging  from  the  figures  given,  one  can  see 
that  the  cost  of  flotation  for  various  processes, 
localities,  and  ores  varies  greatly.  To  get  the 
cost  of  flotation  for  any  particular  ore,  Stander 
gives  the  following  items,1  which  if  taken  into 
consideration  should  give  an  approximate  result : 
power;  oil,  acid,  or  both;  royalty,  if  any;  labor; 
supplies  and  repair  work;  heat  (if  a  hot  solu- 
tion is  required). 

1  "The  Flotation  Process,"  by  Stander,  1916. 


CHAPTER  VIII 
FORMULAS  AND  TABLES 

Estimation  of  Consumption  of  Oil  and  Acid 
per  Ton  of  Feed 

The  following  is  a  useful  chart  whereby  the 
consumption  of  oil  and  acid  can  be  estimated 
per  ton  of  feed.1 

A  concrete  example  showing  how  to  use  the 
table  may  not  be  amiss:  Assume  that  a  plant 
treats  450  tons  per  24  hr.  and  that  the  con- 
sumption of  pine-oil  is  160  cc.  per  minute,  it  is 
desired  to  find  the  consumption  of  pine-oil  in 
pound  per  ton  of  feed. 

From  the  point  of  intersection  of  the  100 
cc.  per  minute  line  and  the  pine-oil  line,  follow 
down  and  read  the  figure  2.95,  which  would  be 
the  consumption  in  pound  per  ton  at  100  cc.  per 
minute,  and  100  tons  of  feed  per  24  hr. 

Inasmuch  as  the  consumption  of  oil  is  greater 
tha^n  100  cc.  per  minute  and  the  tonnage  treated 
is  greater  than  100  tons  per  24  hr.,  we  must  use 
the  third  formula  to  arrive  at  our  final  figure. 
Thus  a 


2.95  X 


2.95  X         X         =  1.05  lb.  per  ton. 


. 
450  100 

100 

1  Min.  &  Sci.  Press,  May  20,  1916. 
155 


156 


FORMULAS   AND   TABLES 


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CALCULATION  OF  TONNAGE 


157 


Calculation  of  Tonnage  of  Feed  to  any 
Particular  Unit 

For  the  application  of  this  method  the  tonnage 
of  either  the  concentrate  or  the  tailing  produced 
must  be  known  and  also  the  assay  of  all  three  — 
heads,  tailings,  and  concentrate.  The  basis  of 
the  method  is  the  efficiency  by  assay  of  the 
plant. 

A  concrete  example,  used  in  figuring  the  ton- 
nage to  a  certain  flotation  plant,  in  which  both 
lead  and  a  zinc  concentrate  were  made,  will  be 
clearer  than  the  use  of  formulas  and  unknowns. 

The  concentrate  tonnage  is  known  and  also 
the  assay  (in  zinc)  of  the  heads,  tailing,  and  con- 
centrate. 


Products. 

Assay,  Zn 
per  cent. 

Symbol. 

Feed     .      

5.7 

H 

Tailing  

2.6 

T 

Concentrate 

40  4 

c 

Then: 

Ratio  of  concentration 

C  -  T  ^  40. 4  -2. 6 
"  H-  T~     5.7-2.6 

Efficiency  of  concentration 
C  X  100      40.4  X  100 


12.1. 


HxR       5.7X12.1 


=  58.7  per  cent 


made  211  tons  concentrate  of  40.4  zinc,  which 
equals  85.2  tons  of  metallic  zinc. 


158  FORMULAS  AND  TABLES 

85.2  tons  equals  58.7  per  cent  of  zinc  in  the 
original  feed. 

100  per  cent  —  58.7  per  cent  =  41.3  per  cent 
zinc  lost  in  the  lead  concentrate  and  tailing, 
or  59.9  tons  metallic  zinc. 

85.2  +  59.9  =  145.1  tons  of  metallic  zinc  in 
the  original  feed. 

145.1  -T-  0.57  =  2545.5  tons  of  feed  to  the  plant. 

The  tonnage  of  concentrate  or  tailing  could, 
by  knowing  the  feed  tonnage,  be  equally  well 
calculated  by  this  method. 


CALCULATION  OF  TONNAGE 


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160  FORMULAS  AND  TABLES 

Torque  units  should  be  distinguished  from  energy 
units:  Thus,  foot-pound  and  kilogram-meter  for  energy, 
and  foot-pound  and  meter-kilogram  for  torque. 

1  ft.-lb.1  =  13,560,000  ergs  =  1.356  joules  =  0.3239 
g.-cal.  =  0.1383  kg.-m.  =  0.001285  B.t.u.  =  0.0003766 
watt-hr.  =  0.0000005051  h.p.-hr. 

1  kg.-m.  =  98,060,000  ergs  =  9.806  joules  =  7.233 
ft.-lb.  =  2.34  g.-cal.  =  0.009296  B.t.u.  =  0.002724  watt- 
hr.  =  0.000003704  h.p.-hr.  (metric). 

1  B.t.u.  =  1055  joules  =  778.1  ft.-lb.  =  252  g.-cal.  = 
107.6  kg.-m.  =  0.5555  Ib. -centigrade  heat  unit  =  0.2930 
watt-hr.  =  0.252  kg.-cal.  =  0.0003984  h.p.-hr.  (metric) 
=  0.0003930  h.p.-hr. 

1  watt-hr.  =  3600  joules  =  2655.4  ft.-lb.  =  860  g.-cal. 
=  367.1  kg.-m.  =  3.413  B.t.u.  =  0.001341  h.p.-hr. 

1  h.p.-hr.  =  2,684,000  joules  =  1,980,000  ft.-lb.  = 
273,700  kg.-cm.  =  745.6  watt-hr. 

1  kw.-hr.  =  2,655,000  ft.-lb.  =  367,190  kg.-m.  =  1.36 
h.p.-hr.  (metric)  =  1.34  h.p.-hr. 

POWER 

1  g.-cm.  per  sec.  =  0.00009806  watt. 

1  ft.-lb.  per  min.  =  0.02260  watt  =  0.00003072  h.p. 
(metric)  =  0.00000303  h.p. 

1  watt  =  44.26  ft.-lb.  per  min.  =  6.119  kg.-m.  per 
min.  =  0.001  kilowatt. 

1  h.p.  =  33,000  ft.-lb.  per  min.  =  745.6  watts  =  550 
ft.-lb.  per  sec.  =  76.04  kg.-m.  per  sec.  =  1.01387  h.p. 
(metric). 

1  kw.  =  44,256.7  ft.-lb.  per  min.  =  101.979  kg.-m.  per 
sec.  =  1.3597  h.p.  (metric)  =  1.341  h.p. 

RESISTIVITY 

1  ohm  per  cir.  mil-ft.  =  0.7854  ohm  per  sq.  mil-ft. 
=  0.001662  ohm  per  sq.  mm.-m.  =  0.0000001657  ohm 
per  cm.3  =  0.0000000524  ohm  per  in.3 

1  ohm  per  sq.  mil.-ft.  =  1.273  ohms  per  cir.  mil-ft. 
1  The  hyphen  (-)  as  used  here  means  "  multiplied  by." 


WEIGHT  161 

=  0.002117   ohm  per    sq.   mm.-m  =  0.0000002116    ohm 
per  cm.3  =  0.00000008335  ohm  per  in.3 

1  ohm  per  in.3  =  15,280,000  ohms  per  cir.  mil-ft. 
=  12,000,000  ohms  per  sq.  mil-ft.  =  25,400  ohms  per 
sq.  mm.-m.  =  2.54  ohms  per  cm.3 

CURRENT  DENSITY 

1  amp.  per  sq.  in.  =  0.7854  amp.  per  cir.  in.  =  0.1550 
amp.  per  sq.  cm.  =  1,273,000  cir.  mils  per  amp.  =  0.000001 
amp.  per  sq.  mil. 

1  amp.  per  sq.  cm.  =  6.45  amp.  per  sq.  in.  =  197,000 
cir.  mils  per  amp. 

1000  cir.  mils  per  amp.  =  1273  amp.  per  sq.  in. 

1000  sq.  mils  per  amp.  =  1000  amp.  per  sq.  in. 

METRIC   SYSTEM   WITH   CONVERSIONS 

10  milli-  =  1  centi-.  10  deca-  =  1  hecto-. 

10  centi-  =  1  deci-.  10  hecto-  =  1  kilo-. 

10  deci-  =  1  (unit).  1  kilo-  =  1  myria. 
10  (units)  =  1  deca-. 

WEIGHT 

METRIC  UNIT  is  GRAM 

Gram  =  weight  1  cubic  centimeter  of  water  at  4°  C. 
Gram  =  15.4324  grains. 
Gram  =  .03215  ounce  troy. 
-Gram  =  .00267923  pound  troy. 
Gram  =  .03527  ounce  avoirdupois. 
Gram  =  .00220462  pound  avoirdupois. 
Milligram  =  .0154324  grain. 
Kilo  or  kilogram  =  32.15  ounces  troy. 
Kilo  or  kilogram  =  2.67923  pounds  troy. 
Kilo  or  kilogram  =  35.27  ounces  avoirdupois. 
Kilo  or  kilogram  =  2.20462  pounds  avoirdupois. 
Metric  ton  =  1000  kilos  or  kilograms. 
Metric  ton  =  2204.62  pounds  avoirdupois. 
Metric  ton  =  1.10231  United  States  tons  (2000  pounds). 
Grain  =  .0648  gram. 
Ounce  troy  =  31.10348  grams. 


162  FORMULAS  AND   TABLES 

Pound  troy  =  .37324  kilo  or  kilogram. 
Pound  troy  =  373.24  grams. 
Ounce  avoirdupois  =  28.3495  grams. 
Pound  avoirdupois  =  .45359  kilo  or  kilogram. 
Pound  avoirdupois  =  453.59  grams. 
Ton  (2000  pounds)  =  .90718  metric  ton. 
Ton  (2000  pounds)  =  907.185  kilograms. 
Assay  ton  =  29.1666  grams. 
Assay  ton  =  .0377  ounce  troy. 
Assay  ton  =  .07814  pound  troy. 
Assay  ton  =  1 .0287  ounces  avoirdupois. 
Assay  ton  =  .0643  pound  avoirdupois. 

CAPACITY 

METRIC  UNIT  is  LITER 
Liter  =  1000  cubic  centimeters. 
Liter  =  .26417  gallon  (231  cubic  inches). 
Liter  =  1.05668  quarts. 
Liter  =  33.81  liquid  ounces. 
Liter  =  61.023  cubic  inches. 
Gallon  (231  cubic  inches)  =  3.78543  liters. 
Gallon  (231  cubic  inches)  =  3785.43  cubic  centimeters. 
Liquid  ounce  =  .029574. 

VOLUME 

Cubic  meter  =  35.314  cubic  feet. 
Cubic  meter  =  1.3079  cubic  yards. 
Cubic  centimeter  =  .061  cubic  inch. 
Cubic  foot  =  .02832  cubic  meter. 
Cubic  yard  =  .7645  cubic  meter. 

LENGTH 

METRIC  UNIT  is  METER 

Meter  =  39.37  inches.  Inch  =  2.54  centimeters. 

Meter  =  3.280833  feet.  Foot  =  30.48  centimeters. 

Kilometer  =  3280.833  feet.       Foot  =  .3048  meter. 
Kilometer  =  .62137  mile.          Mile  =  1.60935  kilometers. 
Centimeter  =  .3937  inch.          Mile  =  1609.347  meters. 


WEIGHTS  AND   MEASURES  163 

AREA 

Square  meter  =  10.764  square  feet. 
Square  meter  =  1550.3  square  inches. 
Hectare  or  square  hectometer  =  2.4711  acres. 
Square  kilometer  =  247.1  acres. 
Square  inch  =  6.452  square  centimeters. 
Square  foot  =  929  square  centimeters. 
Square  foot  =  .0929  square  meter. 
Square  mile  =  2.59  square  kilometers. 
Acre  =  .40469  hectare. 
Acre  =  4046.9  square  meters. 


UNITED   STATES   WEIGHTS  AND   MEASURES 
AVOIRDUPOIS  WEIGHT 

27.34375  grains  =  1  dram. 

16  drams  =  1  ounce  (oz.). 

437.5  grains  =  1  ounce. 

16  ounces  =  1  pound  (lb.). 

7000  grains  =  1  pound.    ' 

100  pounds  =  1  hundredweight. 

2000  pounds  =  1  short  ton  (usually  used). 

2240  pounds  =  1  long  ton  (seldom  used). 

TROY  WEIGHT 

24  grains  =  1  pennyweight  (dwt.). 
20^  pennyweights  =  1  ounce  (oz.). 
480  grains  =  1  ounce. 
12  ounces  =  1  pound  (lb.). 
5760  grains  =  1  pound. 

APOTHECARIES'  WEIGHT 

20  grains  =  1  scruple.  480  grains  =  1  ounce. 

3  scruples  =  1  dram.  12  ounces  =  1  pound. 

8  drams  =  1  ounce.  5760  grains  =  1  pound. 


164  FORMULAS  AND  TABLES 

• 

LENGTH 
12  inches  =  1  foot.  4  rods  =  1  chain. 

3  feet  =  1  yard.  66  feet  =  1  chain. 
5|  yards  =  1  rod.                       320  rods  =  1  mile. 
16J  feet  =  1  rod.                        5280  feet  =  1  mile. 

AREA 

144  square  inches  =  1  square  foot. 
9  square  feet  =  1  square  yard. 
30J  square  yards  =  1  square  rod. 
160  square  rods  =  1  acre. 
640  acres  =  1  square  mile. 

VOLUME 

1728  cubic  inches  =  1  cubic  foot. 
27  cubic  feet  =  1  cubic  yard. 

CAPACITY 

Liquid 

4  gills  =  1  pint. 

2  pints  =  1  quart. 

4  quarts  =  1  gallon  (231  cubic  inches). 

63  gallons  =  1  hogshead. 

31J  gallons  =  1  barrel 

Dry 

2  pints  =  1  quart. 

4  quarts  =  1  gallon  (268.8025  cubic  inches). 
2  gallons  =  1  peck. 
4  pecks  =  1  bushel  (2150.42  cubic  inches). 

AVOIRDUPOIS  AND   TROY  CONVERSIONS 

Ounce  troy  =  1.09714  ounces  avoirdupois. 
Pound  troy  =  13.166  ounces  avoirdupois. 
Pound  troy  =  .822857  pound  avoirdupois. 
Ounce  avoirdupois  =  .91145  ounce  troy. 
Pound  avoirdupois  =  14.583  ounces  troy. 
Pound  avoirdupois  =  1.21528  pounds  troy. 


THERMOMETER  READINGS  165 

Ton  (2000  pounds  avoirdupois)  =  29,166f  ounces  troy. 
Ton  (2000  pounds  avoirdupois)  =  2430.56  pounds  troy. 

MONEY 

ENGLISH 

4  farthings  =  1  penny  (d).        1    pound  =  7.3224    grams 
4  pence  =  1  shilling  (s).  gold. 

20  shillings  =  1  pound  (£).       1  pound  =  $4.8665  United 
1   pound  =  113.001    grains          States  money, 
gold. 

MEXICAN 

100  centavos  =  1  peso.  1  peso  =  .87  or  J  troy  ounce 

1  peso  =  417.74  grains  sil-          (approximate)  silver, 
ver.  1  peso  =  27.073  grams  sil- 

ver. 

UNITED  STATES  >•"'*., 

100  cents  =  1  dollar  ($).  1  dollar  =  23.22  grains  gold. 

VALUE  OF  GOLD 

1  ounce  troy  =  $20.67. 

1  pennyweight  (dwt.)  =  ^  ounce  troy. 

1  pennyweight  =  $1.03^. 

1  grain  =  4.306  cents  (United  States). 

1  gram  =  $0.6646. 

1  gram  =  .03215  or  ^T  (approximate)  ounce  troy. 

1  kilo  =  $664.60. 

1  kilo  =  32.15  ounces  troy. 

CONVERSION   OF  THERMOMETER  READINGS 


Freezing  point. 

Boiling  point. 

Fahrenheit   

degrees. 

degrees. 
01  o 

Centigrade  

32 

212 

1  /-v/-v 

0 

1UU 

To  convert  Fahrenheit  to  Centigrade,  subtract  32  and 
multiply  by  f . 


166 


FORMULAS  AND  TABLES 


To  convert  Centigrade  to  Fahrenheit,  multiply  by  f 
and  add  32. 

WEIGHT   AND   MEASURE   OF  WATER 

1  pound  (avoirdupois)  water  =  27.68122  cubic  inches. 
1  pound  (avoirdupois)  water  =  .0160192  cubic  foot. 
1  gallon  (United  States  liquid)  water  =  231  cubic  inches. 
1  gallon  (United  States  liquid)  water  =  .13368  cubic  foot. 
1  gallon  (United  States  liquid)  water  =  3.78543  liters. 
1  gallon   (United    States    liquid)   water  =  8.3389  pounds 

(avoirdupois). 

1  cubic  foot  water  =  62.42  pounds  (avoirdupois). 
1  cubic  foot  water  =  7.48052  gallons. 
1  cubic  foot  water  =  28.318  liters. 
1  ton  water  =  339.84  gallons. 
1  ton  water  =  32.941  cubic  feet. 
1  ton  water  =  907.2  liters. 
1  liter  water  =  2.2046  pounds  (avoirdupois). 

WEIGHT   OF   ROCK  AND    SAND 


Cubic  feet 
per  ton. 

Weight  in 
pounds  per 
cubic  foot. 

Sulphide  ore  in  place  

11-13 

182-154 

Sulphide  ore  broken 

15-18 

133-111 

Oxidized  ore  in  place 

14-18 

143-111 

Oxidized  ore  broken  

22-24 

91-81 

Quartz  in  place.     (Specific  grav- 
ity, 2.65)    

12 

165 

Quartz  broken  

21 

94 

Earth  in  bank 

18 

111 

Earth,  dry  and  loose       

27 

74 

Clay  

17 

118 

Loose  sand 

25 

80 

Mill  tailing.     (Specific  gravity, 
2.7) 
Sand  collected  under  water  
Transferred       sand       (before 
leaching)  

21.5 
26 

93 

77 

Leached  sand  (that  has  been 
transferred)  

24 

83.3 

AUTOMATIC  WEIGHTS,    1917 


167 


INTERNATIONAL  ATOMIC  WEIGHTS,   1917 


Element. 

Sym- 
bol. 

Atomic 
weight. 

Element. 

Sym- 
bol. 

Atomic 
weight. 

Aluminium  
Antimony 

Al 
Sb 

27.1 
120  2 

Neodymium  
Neon 

Nd 

Ne 

144.3 
20  2 

Argon 

A 

39.88 

Nickel 

Ni 

58  68 

Arsenic  

As 

74.96 

Niton  (radium  em- 

Barium   

Ba 

137.37 

anation) 

Nt 

222.4 

Bismuth  

Bi 

208.0 

Nitrogen  

N 

14.01 

Boron  . 

B 

11.0 

Osmium  

Os 

190.9 

Bromine 

Br 

79.92 

Oxvgen 

o 

16  00 

Cadmium 

Cd 

112.40 

Palladium  .  . 

Pd 

106.7 

Ccesium  .  . 

Cs 

132.81 

Phosphorus.  .  .  . 

P 

31.04 

Calcium 

Ca 

40  07 

Platinum 

Pt 

195  2 

Carbon  .  . 

c 

12.005 

Potassium 

K 

39  10 

Cerium  

Ce 

140.25 

Praseodymium  .  . 

Pr 

140.9 

Chlorine  

Cl 

35.46 

Radium  

Ra 

226.0 

Chromium 

Cr 

52.0 

Rhodium 

Rh 

102  9 

Cobalt  
Columbium  

Co 
Cb 

58.97 
93.1 

Rubidium  
Ruthenium  

Rb 

Ru 

85.45 
101.7 

Copper  . 

Cu 

63.57 

Samarium 

Sa 

150  4 

Dysprosium  

Dy 

162.5 

Scandium  

Sc 

44  1 

Erbium 

Er 

167  7 

Selenium 

Se 

79  2 

Europium  

Eu 

152.0 

Silicon 

Si 

28  3 

Fluorine  

F 

19.0 

Silver.  

Ag 

107  88 

Gadolinium  

Gd 

157  3 

Sodium  

Na 

23  00 

Gallium  

Ga 

69.9 

Strontium 

Sr 

87  63 

Germanium  

Ge 

72.5 

Sulphur  

s 

32  06 

Glucinum.. 

Gl 

9  1 

Tantalum 

Ta 

181  5 

Gold-.  .  . 

Au 

197  2 

Tellurium 

Te 

127  5 

Helium  

He 

4.00 

Terbium  

Tb 

159  2 

Holmium  

Ho 

163  5 

Thallium 

Tl 

204  0 

Hydrogen.  * 

H 

1  008 

Thorium 

Th 

232  4 

Indium  

In 

114  8 

Thulium 

Tin 

168  5 

Iodine  

I 

126.92 

Tin     . 

Sn 

118  7 

Iridium  

Ir 

193  1 

Titanium 

Ti 

48  1 

Iron  

Fe 

55  84 

Tungsten 

W 

184  0 

Krypton  

Kr 

82  92 

Uranium 

u 

238  2 

Lanthanum  

La 

139  0 

Vanadium 

V 

51  0 

Lead  

Pb 

207  20 

Xenon 

Xe 

130  2 

Lithium 

Li 

6  94 

Ytterbium      (Neo- 

Lutecium.  . 

Lu 

175  0 

ytterbium) 

Yb 

173  5 

Magnesium  
Manganese  

Mg 
Mn 

24.32 
54  93 

Yttrium  
Zinc 

Yt 
Zn 

88.7 
65  37 

Mercury 

Hg 

200  6 

Zr 

90  6 

Molybdenum  

Mo 

96.0 

168 


FORMULAS  AND  TABLES 


MAXIMUM   SOLUBILITIES 
(!N  WATER  AT  ORDINARY  TEMPERATURES) 

Parts  in  water. 

Aluminum  sulphate  (A12  (864)3) 1  part  in  3. 

Calcium  carbonate  (CaCOs) Insoluble. 

Calcium  chloride  (CaCl2) 1  part  in  If. 

Calcium  hydroxide  (slacked  lime  — Ca(OH)3) .  600. 

Calcium  oxide  (unslacked  lime  —  CaO) 800. 

Calcium  sulphate  (CaSO4) "       500. 

Calcium  sulphite  (CaSOs) nsoluble. 

Copper  sulphate  (CuSOi) part  in  4. 

Iron  oxide,  hydroxide,  and  sulphide nsoluble. 

Iron  sulphate  (copperas  —  FeSO4) part  in  4. 

Lead  acetate  (Pb  (C2H3O2)2) "       2. 

Lead  carbonate  (PbCOs)    nsoluble. 

Lead  oxide  (litharge  —  PbO) 

Lead  sulphate  (PbSO4) 

Lead  sulphite  (PbSO3) 

Lead  chloride  (PbCl2) 1  part  in  93. 

Magnesium  sulphate  (MgSCh) 1                  3. 

Mercuric  chloride  (HgCl2) 15. 

Oxalic  acid  (C2O4H2  •  2  H2O) 10£. 

Potassium  bicarbonate  (KHCOs) 3. 

Potassium  carbonate  (K2CO3) 1. 

Potassium  cyanide  (KCN) I  (boiling). 

Potassium  ferrocyanide  (K4Fe(CN)6) 3£. 

Potassium  hydroxide  (KOH) 1. 

Potassium  iodide  (KI) "         |. 

Potassium  sulphate  (K2SO4) 9. 

Silver  nitrate  (AgNOs) ft. 

Sodium  bicarbonate  (NaHCOs) 1       "       10. 

Sodium  bisulphate  (NaHSCM 1                 3£. 

Sodium  carbonate  (Na2CO3) 1                  4. 

Sodium  hydroxide  (NaOH) 1                  1. 

Sodium  sulphate  (Na2SO4) 1                  4. 

Zinc  carbonate  (ZnCOs) Insoluble. 

Zinc  cyanide  (Zn(CN)2) 

Zinc  hydroxide  (Zn(OH)2) 

Zinc  sulphate  (Zn(SO)4) 1               If. 


FORMULAS  FOR  CIRCLES  AND  CIRCULAR  TANKS 

Circumference  of  circle  =  diameter  X  3.1416. 

.    .    .         diameter2 
Area  of  circle  = = X  3.1416. 

a 

Volume  of  cylindrical  tank  =  area  of  bottom  X  height. 


Volume  of  cone  = 


area  of  base  X  height 


INDEX 

PAGE 

Acidity  and  alkalinity 118 

Acid,  probable  effect  on  flotation 118 

Adhesion 46 

Adsorption 44 

explanation  of 44 

and  absorption 44 

in  flotation 44 

temperature  and  pressure  upon 46 

Amount  of  frothing  agent  in  tests 116 

Apparatus  for  measuring  oil  added  in  tests 123 

Bubbles,  basic  factor  in  making 20 

Bubbles 92 

bursting  of,  cause,  etc 92-93 

Callow  test  set 146-149 

Calculation  of  tonnage  of  feed  to  any  particular  unit     157 

Capillary  attraction 34 

phenomena 34 

attraction,  result  of 36 

Case  testing  machine 143 

Coal-tar  creosote,  character  of  froth 99 

Coal-tar  products 87-88 

Coal-tar  cresols 88 

Colloids ; . .         8 

terminology  of 8-10 

chemistry,  concept  of 10-12 

classification  of 13 

properties  of 14 

condition,  control  of 19 

Contact  angle ' 28 

definition  of 28 

in  flotation 29-33 

169 


170  INDEX 

PAGE 

Cost  of  flotation 151-154 

Cresol,  or  cresylic  acid  froths 101 

Crude-wood,  turpentines 89 

Dealers  in  flotation 104-106 

Dineric  interface 50 

Disposal  of  froth 125 

Effect  of  temperature  on  flotation  tests 119 

Effect   of  addition   agents  in  flocculating   ganguc- 

slimes 120-121 

Electric  charges  on  suspended  particles 43 

Electrical  phenomena  in  flotation 53-64 

Electrical  theory,  requirements  for 53 

Electrification  of  bubbles 55 

Electrical  theory,  Ralston's 57 

Callow's 57 

Baines' 53-56 

DurelPs  objection  to 57 

Fahrenwald's  experiments 58-64 

Emulsification 48 

effect  upon  flotation 48 

theory  of 49-51 

Emulsion,  definition  of 48 

modifying  agents 49 

Equation  of  Gibbs 45 

Film  flotation 126 

Filters,  size  of  pores  in 15 

Flotation,  concentration  by 1 

definition  of 2 

Flotation  processes,  classification  of 4 

Flotation,  theory  of 7 

oils  used  in 87 

of  oxidized  ores  by  use  of  hydrogen  sulphide .....  80 

by  use  of  sulphur  vapor 82 

by  various  solutions 81 

by  use  of  sulphuretted  oil 83 

by  use  of  colloidal  sulphur 83 

by  the  Murex  magnetic  process 83-85 


INDEX  171 

PAGE 

Flotation  oils,  cost  of 106-108 

consumption  of  in  the  United  States 109 

Forms  for  flotation  tests 117-118 

Formulas  and  tables,  chapter  on 155 

Froths  and  bubbles 92-93 

Froths  formed  by  flotation  oils 93-95 

Froths,  disposal  of 125 

Frothing  agents  in  tests,  amounts  used 116 

Fuel-oil 88 

Gas-oils 89 

Grinding  for  flotation  tests 112-115 

Grinding  for  flotation,  fineness  of 115 

Hoover  testing  machines 138-140 

Interfacial  tension 47 

Iron  pipe  mill 115 

Janney  test  machine 131-138 

Kinds  of  frothing  agents 116 

Macquisten  tube 127 

Mechanical  frothing  apparatus 131-138 

Mohr  pipette 123 

Oils  and  other  reagents  in  flotation 86 

used  in  flotation 56-57 

collectors  or  oilers : . . .  89 

f rothers  or  f earners 89 

Oxidized  ores 79 

the  flotation  of 59 

classification  of  methods 59-60 

Osmosis 37-38 

definition  of 37 

relations  to  colloids 38-39 

Osmotic  phenomena 37 

pressure,  influence  of  added  substances  upon 39 


172  INDEX 

PAGE 

Preferential  flotation 64 

vs.  selective  flotation 64 

classification  of  methods 65 

roasting  processes 65-70 

by  use  of  a  chemical  solution 70-72 

controlling  methods 72-77 

furnishes  new  evidence  to  strengthen  electrical 

theory 74-78 

Pebble  mill 114 

Pine-oil,  characteristics  of  froth 96-99 

Pneumatic  flotation  test  apparatus 146-150 

Potter-Delprat  apparatus 130 

Roy  and  Titcomb  test  machine 145 

Separatory  funnels  for  testing 146 

Slide  machine  for  testing 140-142 

Speed  of  agitation  in  tests 119 

Surface  films 25 

Surface  tension 20 

definition  of 20 

effects  of  added  substances  upon 20-23 

phenomena . 23-24 

the  force  of 24 

effect  of  oil  on , 28 

Suspensoids  and  emulsoids 17 

properties  of 17 

Tables,  chapter  of 155 

Tests. 110 

important  points  t9  test  for 110 

preliminary  considerations 110 

methods  of  grinding  for 110-113 

effect  of  temperature  upon 119 

acidity  and  alkalinity  in 118 

amount  of  frothing  agent  in 116 

fineness  of  grinding  for 115 

addition  agents  in 120 

speed  of  agitation  for 119 

Test  tubes  for  flotation. .                                129 


INDEX  173 

PAGE 

The  purpose  of  oil  in  flotation 89 

The  qualities  of  flotation  oil 90-92 

The  cost  of  flotation  oils 106-107 

Types  of  machines  and  their  operation 126 

classification  of 126 

Viscosity 39-44 

examples  illustrating 40 

molecular  dispersoids 42 

suspensoids 43 

Wood  creosote  bubbles 100 

Wood-testing  machines 128 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

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